Powder Diffraction and Rietveld Refinement School 2020
Dear All, The biennial Powder Diffraction & Rietveld Refinement School at Durham University will take place 29th March-2nd April 2020. The information about the School content and format, practical information (deadlines and fees) and the application link are available at: https://community.dur.ac.uk/john.evans//webpages/pdrr_school.htm<https://community.dur.ac.uk/john.evans/webpages/pdrr_school.htm> As in previous years, we will offer a combination of lectures covering the theoretical aspects of powder diffraction and Rietveld refinement, classroom-based "by-hand" problem sessions/tutorials and extensive hands-on practical sessions using a variety of modern software packages. Topics to be covered will include: * Data collection strategies for X-ray and neutron diffraction * Constant-wavelength and time-of-flight diffraction * Modelling peak shapes (including microstructure analysis) * Indexing powder patterns * Rietveld, Le Bail and Pawley fitting methods * X-ray and neutron combined Rietveld refinements * Restrained refinements * Rigid body refinements * A number of more specialised and advanced optional topics (ab-initio structure solution, parametric and symmetry distortion mode refinements) Lectures will be given by Prof. John Evans, Prof. Ivana Evans, Dr. Jeremy Cockcroft and Prof. Andy Fitch. Best wishes, Ivana Evans Ivana Radosavljevic Evans Professor in Structural/Materials Chemistry Royal Society - Leverhulme Senior Research Fellow Durham University Department of Chemistry Durham DH1 3LE, U.K. Phone: (0191) 334-2594 www.dur.ac.uk/chemistry/research/academic-groups/i.r.evans/<http://www.dur.ac.uk/chemistry/research/academic-groups/i.r.evans/> Twitter: @ivana_evans ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
2018 Powder Diffraction & Rietveld Refinement School, Durham
Dear All, The biennial Powder Diffraction & Rietveld Refinement School at Durham University will take place 8-12th April 2018. The applications deadline is approaching - online applications can be submitted until the end of next week, 19 January 2018, at the School website: community.dur.ac.uk/john.evans/webpages/riet_register.htm<https://community.dur.ac.uk/john.evans/webpages/riet_register.htm> As in previous years, we will offer a combination of lectures covering the theoretical aspects of powder diffraction and Rietveld refinement, classroom-based "by-hand" problem sessions/tutorials and extensive hands-on practical sessions using a variety of modern software packages. Topics to be covered will include: * Data collection strategies for X-ray and neutron diffraction * Constant-wavelength and time-of-flight diffraction * Modelling peak shapes (including microstructure analysis) * Indexing powder patterns * Rietveld, Le Bail and Pawley fitting methods * X-ray and neutron combined Rietveld refinements * Restrained refinements * Rigid body refinements * A number of more specialised and advanced optional topics (ab-initio structure solution, parametric and symmetry-mode refinements) Lectures will be given by Prof. John Evans, Dr. Ivana Evans, Dr. Jeremy Cockcroft and Prof. Andy Fitch. Best wishes, Ivana Evans Dr. Ivana Radosavljevic Evans Associate Professor/Reader in Structural/Materials Chemistry Durham University Department of Chemistry Durham DH1 3LE, U.K. Office: CG 244 Phone: (0191) 334-2594 www.dur.ac.uk/chemistry/research/academic-groups/i.r.evans/<http://www.dur.ac.uk/chemistry/research/academic-groups/i.r.evans/> ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
2018 Powder Diffraction & Rietveld Refinement School, Durham
Dear All, The biennial Powder Diffraction & Rietveld Refinement School at Durham University will take place 8-12th April 2018. As in previous years, we will offer a combination of lectures covering the theoretical aspects of powder diffraction and Rietveld refinement, classroom-based "by-hand" problem sessions/tutorials and extensive hands-on practical sessions using a variety of modern software packages. Topics to be covered will include: * Data collection strategies for X-ray and neutron diffraction * Constant-wavelength and time-of-flight diffraction * Modelling peak shapes (including microstructure analysis) * Indexing powder patterns * Rietveld, Le Bail and Pawley fitting methods * X-ray and neutron combined Rietveld refinements * Restrained refinements * Rigid body refinements * A number of more specialised and advanced optional topics (ab-initio structure solution, parametric and symmetry-mode refinements) Lectures will be given by Prof. John Evans, Dr. Ivana Evans, Dr. Jeremy Cockcroft and Prof. Andy Fitch. Online applications can be submitted until 19 January 2018 at the Powder Diffraction & Rietveld Refinement School 2018 website: community.dur.ac.uk/john.evans/webpages/riet_register.htm<https://community.dur.ac.uk/john.evans/webpages/riet_register.htm> Best wishes, Ivana Evans Dr. Ivana Radosavljevic Evans Associate Professor/Reader in Structural/Materials Chemistry Durham University Department of Chemistry Durham DH1 3LE, U.K. Office: CG 244 Phone: (0191) 334-2594 www.dur.ac.uk/chemistry/research/academic-groups/i.r.evans/<http://www.dur.ac.uk/chemistry/research/academic-groups/i.r.evans/> ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
Announcement of 2017 school "Modern Methods in Rietveld Refinement and Structural Analysis"
We are pleased to announce that the third annual "Modern Methods in Rietveld Refinement for Structural Analysis" school will be held from June 18-23, 2017, at Oak Ridge National Laboratory in close partnership with the Shull-Wollan Center Joint Institute for Neutron Sciences (University of Tennessee and ORNL) and Bruker-AXS. The primary goal of this school is to teach participants Rietveld refinement and other methods for evaluating crystal structures from powder diffraction data with an emphasis on data collected on US national user facility beamlines optimized for structural analysis such as the 11-BM, 17-BM, and 11-ID-B synchrotron beamlines at the APS of Argonne National Laboratory, the POWGEN and NOMAD time-of-flight neutron diffraction beamlines at the SNS of Oak Ridge National Laboratory, and the XPD synchrotron beamline at the NSLS-II of BNL. The combination of advances in instrumentation and in software algorithms now allow many challenging structural problems to be resolved solely from powder diffraction data, and an up-to-date instruction in modern methods will be provided. This course will emphasize traditional solid state compounds (non-molecular), and will use the TOPAS software as the platform for Rietveld refinement (complementary trial license will be provided to participants). There will be a special secondary emphasis this year on the complementary use of pair distribution function (PDF) data to carry out small-box refinements for average unit cells, highlighting the new functionality of the TOPAS software to carry out both Rietveld and PDF refinements. Both NOMAD (neutron PDF) and 11-ID-B (synchrotron PDF) beamline scientists will be present as instructors at the course, and there will be an opportunity for participants to have data suitable for both Rietveld and PDF refinement collected on their own sample at both synchrotron and neutron beamlines. Confirmed 2017 instructors include Prof. Peter Khalifah (SBU), Prof. Cora Lind (U. Toledo), Dr. Katharine Page (ORNL, NOMAD), Dr. Ashfia Huq (ORNL, POWGEN), Dr. Jue Liu (ORNL), Dr. Karena Chapman (ANL, 11-ID-B), Dr. Saul Lapidus (ANL, 11-BM), Dr. Wenqian Xu (ANL, 17-BM), and Dr. Nathan Henderson (Bruker-AXS). Further general information about the course is available through the website: https://sites.google.com/a/stonybrook.edu/mmrrsa-portal/. The application for this year can be directly accessed at: http://conference.sns.gov/mmrrsa. There will be no registration fee associated with this course. There are ongoing fundraising efforts to additionally support some or all of the lodging and meal expenses of most or all participants in this program. All travel expenses will be the responsibility of participants. While this course is open to all applicants, priority will be given to Ph.D. students and post-doctoral researchers from North American institutions. Completed applications should be received by March 31, 2017, although later applications may still be considered. Dr. Peter Khalifah, kp...@bnl.gov<mailto:kp...@bnl.gov> Associate ProfessorChemist Dept. of Chemistry Dept. of Chemistry Stony Brook University Brookhaven National Laboratory Stony Brook, NY 11794-3400 Upton, NY 11973-5000 Office: 447 Grad. ChemistryOffice: Bldg 555, Rm 340 Phone: (631)632-7796 Phone: (631)344-7689 Fax: (631)632-7960 Fax: (631)344-5815 Web page: https://sites.google.com/a/stonybrook.edu/pgk/home ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
Second announcement: Powder Diffraction & Rietveld Refinement School, Durham 2016
Dear All, The biennial Powder Diffraction & Rietveld Refinement School at Durham University will take place 10-14th April 2016. As in previous years, we will offer a combination of lectures covering the theoretical aspects of powder diffraction and Rietveld refinement, classroom-based "by-hand" problem sessions/tutorials and extensive hands-on practical sessions using a variety of modern software packages. Topics to be covered will include: * Data collection strategies for X-ray and neutron diffraction * Constant wavelength and time of flight diffraction * Modelling peak shapes (including microstructure analysis) * Indexing powder patterns * Rietveld, Le Bail and Pawley fitting methods * X-ray and neutron combined Rietveld refinements * Restrained refinements * Rigid body refinements * A number of more specialised and advanced optional topics (ab-initio structure solution, parametric and symmetry-mode refinements) Lectures will be given by Prof. John Evans, Dr. Ivana Evans, Dr. Jeremy Cockcroft and Prof. Andy Fitch. Online applications can be submitted until 22nd January 2016, at the Powder Diffraction & Rietveld Refinement School 2016 website: http://community.dur.ac.uk/john.evans/webpages/pdrr_school_2016.htm Best wishes, Ivana Evans Dr. Ivana Radosavljevic Evans Reader in Structural/Materials Chemistry Department of Chemistry Durham University Durham DH1 3LE, U.K. Office: CG 244 Phone: (0191) 334-2594 Fax: (0191) 384-4737 www.dur.ac.uk/chemistry/research/academic-groups/i.r.evans/<http://www.dur.ac.uk/chemistry/research/academic-groups/i.r.evans/> ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
2016 Powder Diffraction & Rietveld Refinement School, Durham
Dear All, The biennial Powder Diffraction & Rietveld Refinement School at Durham University will take place 10-14th April 2016. As in previous years, we will offer a combination of lectures covering the theoretical aspects of powder diffraction and Rietveld refinement, classroom-based "by-hand" problem sessions/tutorials and extensive hands-on practical sessions using a variety of modern software packages. Topics to be covered will include: * Data collection strategies for X-ray and neutron diffraction * Constant wavelength and time of flight diffraction * Modelling peak shapes (including microstructure analysis) * Indexing powder patterns * Rietveld, Le Bail and Pawley fitting methods * X-ray and neutron combined Rietveld refinements * Restrained refinements * Rigid body refinements * A number of more specialised and advanced optional topics (ab-initio structure solution, parametric and symmetry-mode refinements) Lectures will be given by Prof. John Evans, Dr. Ivana Evans, Dr. Jeremy Cockcroft and Prof. Andy Fitch. Online applications can be submitted until 22nd January 2016, at the Powder Diffraction & Rietveld Refinement School 2014 website: http://community.dur.ac.uk/john.evans/webpages/pdrr_school_2016.htm Best wishes, Ivana Evans Dr. Ivana Radosavljevic Evans Reader in Structural/Materials Chemistry Department of Chemistry Durham University Durham DH1 3LE, U.K. Office: CG 244 Phone: (0191) 334-2594 Fax: (0191) 384-4737 www.dur.ac.uk/chemistry/research/academic-groups/i.r.evans/<http://www.dur.ac.uk/chemistry/research/academic-groups/i.r.evans/> ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
RE: information for rietveld refinement
Dear All, Could you please provide the information on low density materials, which has a specific gravity from 0.2 to 0.5 (or. The density 0.2 to 0.5 gr/cc). If you are aware the crystal structure of date seed powder, could you please send it to me. Thanks, and best wishes Husin Husin Sitepu, PhD<http://scholar.google.com/citations?hl=en&user=cUTV8HkJ&view_op=list_works&pagesize=100> Saudi Aramco Research and Development Center Technical Services Division Advanced Analysis Unit Bld. 2296, Room: GB-110 Phone: 876-3050 Email: sitep...@aramco.com<mailto:sitep...@aramco.com> http://scholar.google.com/citations?hl=en&user=cUTV8HkJ&view_op=list_works&pagesize=100 From: alan.he...@gmail.com [mailto:alan.he...@gmail.com] On Behalf Of Alan Hewat Sent: Wednesday, July 16, 2014 9:43 AM To: rietveld_l@ill.fr Subject: Re: information for rietveld refinement > Im student researcher I need a guidelines for refinement structure double > perovskite > using fullprof or other software in case to reduce Factors and than draw > structures Dear Colleague. It is difficult to reply to such a general query. You could start by reading the FullProf manual and tutorials on https://www.ill.eu/sites/fullprof/php/tutorials.html :-) The first question is the symmetry (space group). Do a google search for: https://www.google.com/webhp?q=%22double+perovskite%22+symmetry Then look in particular at the free articles on http://www.researchgate.net/ (3rd link) To search for examples of double perovskites, try http://www.ill.fr/ Log on as "demo" and search for Element=O6 and ElementCount=3 i.e. http://icsd.ill.eu/icsd/index.php?action=Search&elements=o6&elementc=3 If you then click on the formula eg Cu (Nb2 O6) the structure will be drawn using Java in a new window. (You must install Java in your browser and give it permission to run). You can download the CIF files, calculate bond lengths, draw the powder patterns etc by clicking on those buttons. I hope this will get you started, but then I suggest you join the Rietveld mailing list, which has over 1000 members who can advise you about specific problems. To join, send an email to mailto:lists...@ill.fr>> with the title: SUBSCRIBE Rietveld_L "your name and lab" With kind regards, Alan Hewat (Rietveld list manager) __ Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE mailto:alan.he...@neutronoptics.com>> +33.476.98.41.68 http://www.NeutronOptics.com/hewat __ The contents of this email, including all related responses, files and attachments transmitted with it (collectively referred to as “this Email”), are intended solely for the use of the individual/entity to whom/which they are addressed, and may contain confidential and/or legally privileged information. This Email may not be disclosed or forwarded to anyone else without authorization from the originator of this Email. If you have received this Email in error, please notify the sender immediately and delete all copies from your system. Please note that the views or opinions presented in this Email are those of the author and may not necessarily represent those of Saudi Aramco. The recipient should check this Email and any attachments for the presence of any viruses. Saudi Aramco accepts no liability for any damage caused by any virus/error transmitted by this Email. ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
Re: Quantification and rietveld refinement
Dear Nelson Duarte, Within the help system of HighScore Plus you will find various tutorial examples about Rietveld analyses. Just press the F1-key at any stage in the program to invoke the help system. These tutorials will guide you step by step. In particular I would recommend you to look at the following chapters within the help file: 6. Analysis/Rietveld Analysis and 8. Practical/ Practice Rietveld analysis We tried to contact you personally by email, but have not yet received an answer. Please feel free to contact your local PANAlytical representatives at any time, they will help you further or will get you in touch with a specialist. Sincerely yours, Gwilherm Nénert Gwilherm Nénert - Product Marketing XRD PANalytical B.V. Lelyweg 1 (7602 EA) PO Box 13 7600 AA Almelo CoC Registration No. 06069492, Enschede, The Netherlands T +31 546 534 520 M +31 612726178 gwilherm.nen...@panalytical.com www.panalytical.com PANalytical get insight The information contained in this message is confidential and may be legally privileged. The message is intended solely for the addressee(s). If you are not the intended recipient, you are hereby notified that any use, dissemination, or reproduction is strictly prohibited and may be unlawful. If you are not the intended recipient, please contact the sender by return e-mail and destroy all copies of the original message. From: "Nelson" To: , Date: 09/05/2014 06:47 PM Subject:Quantification and rietveld refinement Sent by:rietveld_l-requ...@ill.fr Dear rietvelds I have some samples, all with the same two phases: alumina and crocoite (PbCrO4) (electrochemical bath). I use Cobalt radiation. Indexing, I use always the same two ICDD files, 74-0323 for alumina and 73-1332 for crocoite. I use software High score plus. Can i use the semiquantification of software for know the quantification of each phase betwen the samples. Wuhere i can find the right cif files for this two phases, for introduce in High score plus and made Rietveld refinement. Where i can find a manual or exemples of how to make a rietveld refinement of this XRD. I don´t have experience of rietveld analysis. Thanks in advances Best regrds Nelson++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++ ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
RE: Quantification and rietveld refinement
You would be well advised to do some background reading on microabsorption as it will be pretty bad with those two phases and limit the accuracy you may realistically expect in your quantification Pam From: rietveld_l-requ...@ill.fr [mailto:rietveld_l-requ...@ill.fr] On Behalf Of Nelson Sent: Friday, September 05, 2014 12:44 PM To: rietveld_l@ill.fr Subject: Quantification and rietveld refinement Dear rietvelds I have some samples, all with the same two phases: alumina and crocoite (PbCrO4) (electrochemical bath). I use Cobalt radiation. Indexing, I use always the same two ICDD files, 74-0323 for alumina and 73-1332 for crocoite. I use software High score plus. Can i use the semiquantification of software for know the quantification of each phase betwen the samples. Wuhere i can find the right cif files for this two phases, for introduce in High score plus and made Rietveld refinement. Where i can find a manual or exemples of how to make a rietveld refinement of this XRD. I don´t have experience of rietveld analysis. Thanks in advances Best regrds Nelson ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
Re: Quantification and rietveld refinement
Dear Nelson, You can also often find structures of interest in the American Mineralogist Crystal Structure database (http://rruff.geo.arizona.edu/AMS/amcsd.php). Both of your phases are listed numerous times in this data base, and you can download cif files. The database is freely available. Regards, Dave On 9/5/2014 1:34 PM, Leopoldo Suescun wrote: Prezado Nelson, You can find CIF files for both alumina and crocoite phases at the Crystallography Open Database (www.crystallography.net <http://www.crystallography.net>) looking for chemical elements. An excellent set of educational material on Rietveld refinement using GSAS+EXPGUI at the APS-11BM site (http://www.aps.anl.gov/Xray_Science_Division/Powder_Diffraction_Crystallography/) and additional resources at http://11bm.xray.aps.anl.gov/resources.html. If you don´t have experience with Rietveld analysis and no-one to ask for advice it may be a painful path to walk alone but there are many books that can be of help such as "The Rietveld Method" by RA Young or "Fundamentals of Powder Diffraction and Structural Characterization of Materials" by Pescharsky and Zavalij... but attending a Rietveld course (such as ICDD Clinics for example) may be of help to start. Finally, but maybe of advanced level, be very careful when extracting weight percentages for both phases from your refinements, if you don´t have perfect control or knowledge of particle sizes for both phases, since the huge difference in absorption coefficients among them may make microabsorption an issue on your quantification work. Best of luck Leo 2014-09-05 13:43 GMT-03:00 Nelson <mailto:nelson.dua...@ipn.pt>>: Dear rietvelds I have some samples, all with the same two phases: alumina and crocoite (PbCrO4) (electrochemical bath). I use Cobalt radiation. Indexing, I use always the same two ICDD files, 74-0323 for alumina and 73-1332 for crocoite. I use software High score plus. Can i use the semiquantification of software for know the quantification of each phase betwen the samples. Wuhere i can find the right cif files for this two phases, for introduce in High score plus and made Rietveld refinement. Where i can find a manual or exemples of how to make a rietveld refinement of this XRD. I don´t have experience of rietveld analysis. Thanks in advances Best regrds Nelson ++ Please do NOT attach files to the whole list Send commands to mailto:lists...@ill.fr>> eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++ -- Dr. Leopoldo Suescun Prof. Agr (Assoc. Prof.) de Física Tel: (+598) 29290705/29249859 Cryssmat-Lab./DETEMA Fax: (+598) 29241906* Facultad de Quimica, Universidad de la Republica ,_. | \ | v- ,' \ | ( \__Montevideo, Uruguay En pleno disfrute del Año Internacional de la Cristalografía 2014 (http://www.iycr2014.org ), (http://www.cristalografia2014.fq.edu.uy) -- David L. Bish Department of Geological Sciences Indiana University 1001 E. 10th St. Bloomington, IN 47405 812-855-2039 ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
Re: Quantification and rietveld refinement
Prezado Nelson, You can find CIF files for both alumina and crocoite phases at the Crystallography Open Database (www.crystallography.net) looking for chemical elements. An excellent set of educational material on Rietveld refinement using GSAS+EXPGUI at the APS-11BM site ( http://www.aps.anl.gov/Xray_Science_Division/Powder_Diffraction_Crystallography/) and additional resources at http://11bm.xray.aps.anl.gov/resources.html. If you don´t have experience with Rietveld analysis and no-one to ask for advice it may be a painful path to walk alone but there are many books that can be of help such as "The Rietveld Method" by RA Young or "Fundamentals of Powder Diffraction and Structural Characterization of Materials" by Pescharsky and Zavalij... but attending a Rietveld course (such as ICDD Clinics for example) may be of help to start. Finally, but maybe of advanced level, be very careful when extracting weight percentages for both phases from your refinements, if you don´t have perfect control or knowledge of particle sizes for both phases, since the huge difference in absorption coefficients among them may make microabsorption an issue on your quantification work. Best of luck Leo 2014-09-05 13:43 GMT-03:00 Nelson : > Dear rietvelds > > > > I have some samples, all with the same two phases: alumina and crocoite > (PbCrO4) (electrochemical bath). I use Cobalt radiation. Indexing, I use > always the same two ICDD files, 74-0323 for alumina and 73-1332 for > crocoite. I use software High score plus. Can i use the semiquantification > of software for know the quantification of each phase betwen the samples. > > Wuhere i can find the right cif files for this two phases, for introduce > in High score plus and made Rietveld refinement. > > Where i can find a manual or exemples of how to make a rietveld refinement > of this XRD. > > I don´t have experience of rietveld analysis. > > > > Thanks in advances > > Best regrds > > Nelson > > ++ > Please do NOT attach files to the whole list > > Send commands to eg: HELP as the subject with no body > text > The Rietveld_L list archive is on > http://www.mail-archive.com/rietveld_l@ill.fr/ > ++ > > > -- Dr. Leopoldo Suescun Prof. Agr (Assoc. Prof.) de Física Tel: (+598) 29290705/29249859 Cryssmat-Lab./DETEMA Fax: (+598) 29241906* Facultad de Quimica, Universidad de la Republica ,_. | \ | v- ,' \ | ( \__Montevideo, Uruguay En pleno disfrute del Año Internacional de la Cristalografía 2014 ( http://www.iycr2014.org ), (http://www.cristalografia2014.fq.edu.uy) ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
Quantification and rietveld refinement
Dear rietvelds I have some samples, all with the same two phases: alumina and crocoite (PbCrO4) (electrochemical bath). I use Cobalt radiation. Indexing, I use always the same two ICDD files, 74-0323 for alumina and 73-1332 for crocoite. I use software High score plus. Can i use the semiquantification of software for know the quantification of each phase betwen the samples. Wuhere i can find the right cif files for this two phases, for introduce in High score plus and made Rietveld refinement. Where i can find a manual or exemples of how to make a rietveld refinement of this XRD. I don´t have experience of rietveld analysis. Thanks in advances Best regrds Nelson ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
Re: information for rietveld refinement
> Im student researcher I need a guidelines for refinement structure double perovskite > using fullprof or other software in case to reduce Factors and than draw structures Dear Colleague. It is difficult to reply to such a general query. You could start by reading the FullProf manual and tutorials on https://www.ill.eu/sites/fullprof/php/tutorials.html :-) The first question is the symmetry (space group). Do a google search for: https://www.google.com/webhp?q=%22double+perovskite%22+symmetry Then look in particular at the free articles on http://www.researchgate.net/ (3rd link) To search for examples of double perovskites, try http://www.ill.fr/ Log on as "demo" and search for Element=O6 and ElementCount=3 i.e. http://icsd.ill.eu/icsd/index.php?action=Search&elements=o6&elementc=3 If you then click on the formula eg Cu (Nb2 O6) the structure will be drawn using Java in a new window. (You must install Java in your browser and give it permission to run). You can download the CIF files, calculate bond lengths, draw the powder patterns etc by clicking on those buttons. I hope this will get you started, but then I suggest you join the Rietveld mailing list, which has over 1000 members who can advise you about specific problems. To join, send an email to with the title: SUBSCRIBE Rietveld_L "your name and lab" With kind regards, Alan Hewat (Rietveld list manager) __ * Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE * +33.476.98.41.68 http://www.NeutronOptics.com/hewat __ ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
Rietveld refinement for beginners: bring your data!
Dear Rietvelders, I would like to bring to your attention the following satellite meeting of the IUCr congress in Montreal. Rietveld refinement for beginners: bring your data! Location InterContinental Montréal 360 Rue Saint Antoine Ouest, Montreal, QC H2Y 3X4, Canada Date August 4th, 2014 Description This satellite meeting sponsored by PANalytical will provide training for non experts in Rietveld method. Theoretical aspects of the Rietveld method will be presented with hands-on tutorials devoted to practical cases using x-ray and neutron data. Trial version of HighScorePlus software 4.0 (valid for 3 month) will be installed on attendees PC. The final session of this satellite meeting will be devoted to real scientific problems where the attendees are asked to bring their own powder diffraction data Price: $ 50 CAD for academic, $ 150 CAD for non academic Website: http://www.panalytical.com/Event/IUCr-satellite-meeting.htm Best Regards, Gwilherm Nénert Gwilherm Nénert - Product Marketing XRD PANalytical B.V. Lelyweg 1 (7602 EA) PO Box 13 7600 AA Almelo CoC Registration No. 06069492, Enschede, The Netherlands T +31 546 534 520 M +31 612726178 gwilherm.nen...@panalytical.com www.panalytical.com PANalytical get insight The information contained in this message is confidential and may be legally privileged. The message is intended solely for the addressee(s). If you are not the intended recipient, you are hereby notified that any use, dissemination, or reproduction is strictly prohibited and may be unlawful. If you are not the intended recipient, please contact the sender by return e-mail and destroy all copies of the original message. ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
Powder Diffraction and Rietveld Refinement School, Durham 2014: approaching deadline
Dear All, The biennial Powder Diffraction & Rietveld Refinement School will take place at Durham University, 30th March - 3rd April March 2014. As in previous years, the course will offer a combination of lectures covering the theoretical aspects of powder diffraction and Rietveld refinement, problem sessions/tutorials and extensive hands-on practical sessions using a variety of modern software packages. Topics to be covered will include: * Data collection strategies for X-ray and neutron diffraction * Constant wavelength and time of flight diffraction * Modelling peak shapes * Indexing powder patterns * Rietveld, Le Bail and Pawley fitting methods * X-ray and neutron combined Rietveld refinement * Restrained refinements * Rigid body refinements Lectures will be given by Prof. John Evans, Dr. Ivana Evans, Dr. Jeremy Cockcroft and Prof. Andy Fitch. For any information not covered on the School website please contact Ivana Evans (ivana.radosavlje...@durham.ac.uk<mailto:ivana.radosavlje...@durham.ac.uk>). Online applications can be submitted until 20th January 2014 at the Powder Diffraction & Rietveld Refinement School 2014 website: http://community.dur.ac.uk/john.evans/webpages/pdrr_school_2014.htm. With best wishes for 2014, Ivana Evans Dr. Ivana Radosavljevic Evans Senior Lecturer in Structural/Materials Chemistry Department of Chemistry Durham University Durham DH1 3LE, U.K. Office: CG 244 Phone: (0191) 334-2594 Fax: (0191) 384-4737 www.dur.ac.uk/chemistry/research/academic-groups/i.r.evans/<http://www.dur.ac.uk/chemistry/research/academic-groups/i.r.evans/> ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
Powder Diffraction and Rietveld Refinement School, Durham 2014
Dear All, The biennial Powder Diffraction & Rietveld Refinement School will take place at Durham University, 30th March - 3rd April March 2014. As in previous years, the course will offer a combination of lectures covering the theoretical aspects of powder diffraction and Rietveld refinement, problem sessions/tutorials and extensive hands-on practical sessions using a variety of modern software packages. Topics to be covered will include: * Data collection strategies for X-ray and neutron diffraction * Constant wavelength and time of flight diffraction * Modelling peak shapes * Indexing powder patterns * Rietveld, Le Bail and Pawley fitting methods * X-ray and neutron combined Rietveld refinement * Restrained refinements * Rigid body refinements Lectures will be given by Prof. John Evans, Dr. Ivana Evans, Dr. Jeremy Cockcroft and Prof. Andy Fitch. For any information not covered on the School website please contact Ivana Evans (ivana.radosavlje...@durham.ac.uk<mailto:ivana.radosavlje...@durham.ac.uk>). Online applications can be submitted until 20th January 2014 at the Powder Diffraction & Rietveld Refinement School 2014 website: http://community.dur.ac.uk/john.evans/webpages/pdrr_school_2014.htm. Best wishes, Ivana Evans Dr. Ivana Radosavljevic Evans Senior Lecturer in Structural/Materials Chemistry Department of Chemistry Durham University Durham DH1 3LE, U.K. Office: CG 244 Phone: (0191) 334-2594 Fax: (0191) 384-4737 www.dur.ac.uk/chemistry/research/academic-groups/i.r.evans/<http://www.dur.ac.uk/chemistry/research/academic-groups/i.r.evans/> ++ Please do NOT attach files to the whole list Send commands to eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++
Powder Diffraction & Rietveld Refinement School 2010: deadline reminder
Dear All, Just a reminder of the approaching applications deadline (31st December) for the Powder Diffraction and Rietveld Refinement School in Durham, UK. The EPSRC/IUCr/PCG-SCMP supported biennial Powder Diffraction and Rietveld Refinement School will take place at Durham University, 18th - 22nd April 2010. The course will offer a combination of lectures covering the theoretical aspects of powder diffraction and Rietveld refinement, problem sessions/tutorials and extensive hands-on practical sessions using a variety of modern software packages. Topics to be covered will include: * Data collection strategies for X-ray and neutron diffraction * Constant wavelength and time of flight diffraction * Modelling peak shapes * Indexing powder patterns * Rietveld, Le Bail and Pawley fitting methods * X-ray and neutron combined Rietveld refinement * Restrained refinements * Rigid body refinements Examples and tutorials will cover both extended and molecular systems. Lectures will be given by Prof. John Evans, Dr. Ivana Evans, Dr. Jeremy Cockroft and Prof. Andy Fitch. Student bursaries will be available to contribute to local costs or travel expenses of applicants from UK academic institutions. We will also offer a number of IUCr bursaries to overseas students. For further information and informal inquiries about the School please contact Ivana Evans (ivana.radosavlje...@durham.ac.uk). Online applications can be submitted until 31st December 2009, at the Powder Diffraction and Rietveld Refinement School 2010 website: http://www.dur.ac.uk/john.evans/webpages/pcg_rietveld_school_2010.htm Ivana Evans Dr. Ivana Radosavljevic Evans Lecturer in Structural/Materials Chemistry Department of Chemistry Durham University Durham DH1 3LE, U.K. Office: CG 244 Phone: (0191) 334-2594 Fax: (0191) 384-4737
Re: Rietveld refinement in TOPAS with parallel beam geometry
Sorry about the confusion on the instrument configuration. I am new to the field of x-ray diffraction. Hopefully this helps. The Bruker D8 uses reflection geometry and a THETA : THETA goniometer, where the x-ray source and detector can be move simultaneously on the arms of the goniometer. The x-ray source is Cu and is directed at a Bruker multipurpose Si Gobel mirror which reflects a parallel beam of Cu K-alpha (1&2) radiation at a 2-bounce Ge(022) analyzer crystal. As I understand it, the analyzer crystal filters our the K-alpha 2 peak, producing monochromatic K-alpha 1radiation. There are no soller slits on the primary side of the instrument. The beam is directed at the specimen and the diffracted beam passes through a set of soller slits and then to the point detector. Thanks, Patrick On Fri, Dec 4, 2009 at 5:59 AM, Cline, James Dr. wrote: > Patrick, > > > From: Patrick Price [patrickpric...@gmail.com] > Sent: Friday, December 04, 2009 6:30 AM > To: Rietveld_l@ill.fr > Subject: Rietveld refinement in TOPAS with parallel beam geometry > > Since this is my first post I will start with a brief introduction. My > name is Patrick Price and I am in my second year of graduate school. > My thesis work involves the investigation of phase equilibria in > perovskites. > > I am using a Bruker D8 Discover diffractometer with parallel beam > geometry. The diffractometer has a Cu K-alpha X-Ray source with a Si > Gobel mirror and a Ge monochromator giving a parallel beam > monochromatic x-ray source. > > This instrument description doesn't make sense. > > Regards, > > Jim > > > The receiving side has Soller slits and a > Tl-doped NaI point detector. I am trying to teach myself how to use > TOPAS to PROPERLY analyze my data using Rietveld refinement > techniques. > > I have recently taken a scan of the NIST line profile 660 LaB6 > standard followed by scans of my perovskite powders using a step size > of 0.02 degrees and scan time of 4 seconds. > > Most of the articles I have read are specific to convergent/divergent > beam geometries and I do not know how much of that information > transfers to parallel beam geometries. If anyone could help me answer > the following questions I would greatly appreciate it. These questions > mainly address which parameters should be refined with the LaB6 > standard when using parallel beam geometry. > 1. I need to use the scan of the LaB6 powders to characterize the > contributions of the instrument to the diffraction profile. Starting > with the emission profile, TOPAS asks for the wavelength, the Area, > and the Lorentz Half Width. First, I assume the wavelength I should be > the more recent Cu Ka wavelength of 0.154059 nm instead of 0.154056 > nm. Second, does Cu Ka have a definite Lorentz HW and “Area” or should > these parameters be refined with the LaB6 diffraction pattern? > 2. Since I have a Ge monochromater I assume the Lorentz polarization > factor should be fixed at 27.3 (Is this correct?). Obviously the > lattice parameters and atomic positions would be fixed. > 3. I read that you should NOT refine both the zero shift error and > sample displacement, and since it is parallel beam I only refine the > zero shift error. Should I refine surface roughness, absorption, or > sample tilt with the LaB6? (Currently I do not refine these) > 4. Am I correct in assuming that I do not have any EQUITORIAL > convolutions (e.g. from slits, FDS, beam spill, VDS) since it is > parallel beam geometry? What about TUBE TAILS? > 5. I am using the Finger_et_al method to refine the AXIAL > convolutions, however I often get a large error associated with the S > value (sample length), even when my GOF is decent (<1.45). Do any of > you know why this would happen? > 6. Should I refine the “Scale” or scale factor. (Currently I do) > 7. IMPORTANT: Originally I was refining the crystallite size but it > always refined to a very small value (~300nm), where as NIST claims > 660 LAB6 should have a mean grain size of a few microns or more. I > assume this happens because the TOPAS is accounting for instrument > caused peak broadening by making the crystallite size smaller than it > actually is in the software. However, when I do refine the grain size > I do get a better fit. Should I leave this unchecked, refine it, or > fix it at a reasonable value of ~2500 nm. > > In summary, currently I am only refining the Lorentz HW and “Area” in > the emission profile, zero shift error, the Finger parameters (S & H), > the scale factor, and nothing else. > I am unsure if I should be refining anything else such as the > crystallite size, tube tails and other forms of equatorial > convergence
RE: Rietveld refinement in TOPAS with parallel beam geometry
Patrick, From: Patrick Price [patrickpric...@gmail.com] Sent: Friday, December 04, 2009 6:30 AM To: Rietveld_l@ill.fr Subject: Rietveld refinement in TOPAS with parallel beam geometry Since this is my first post I will start with a brief introduction. My name is Patrick Price and I am in my second year of graduate school. My thesis work involves the investigation of phase equilibria in perovskites. I am using a Bruker D8 Discover diffractometer with parallel beam geometry. The diffractometer has a Cu K-alpha X-Ray source with a Si Gobel mirror and a Ge monochromator giving a parallel beam monochromatic x-ray source. This instrument description doesn't make sense. Regards, Jim The receiving side has Soller slits and a Tl-doped NaI point detector. I am trying to teach myself how to use TOPAS to PROPERLY analyze my data using Rietveld refinement techniques. I have recently taken a scan of the NIST line profile 660 LaB6 standard followed by scans of my perovskite powders using a step size of 0.02 degrees and scan time of 4 seconds. Most of the articles I have read are specific to convergent/divergent beam geometries and I do not know how much of that information transfers to parallel beam geometries. If anyone could help me answer the following questions I would greatly appreciate it. These questions mainly address which parameters should be refined with the LaB6 standard when using parallel beam geometry. 1. I need to use the scan of the LaB6 powders to characterize the contributions of the instrument to the diffraction profile. Starting with the emission profile, TOPAS asks for the wavelength, the Area, and the Lorentz Half Width. First, I assume the wavelength I should be the more recent Cu Ka wavelength of 0.154059 nm instead of 0.154056 nm. Second, does Cu Ka have a definite Lorentz HW and “Area” or should these parameters be refined with the LaB6 diffraction pattern? 2. Since I have a Ge monochromater I assume the Lorentz polarization factor should be fixed at 27.3 (Is this correct?). Obviously the lattice parameters and atomic positions would be fixed. 3. I read that you should NOT refine both the zero shift error and sample displacement, and since it is parallel beam I only refine the zero shift error. Should I refine surface roughness, absorption, or sample tilt with the LaB6? (Currently I do not refine these) 4. Am I correct in assuming that I do not have any EQUITORIAL convolutions (e.g. from slits, FDS, beam spill, VDS) since it is parallel beam geometry? What about TUBE TAILS? 5. I am using the Finger_et_al method to refine the AXIAL convolutions, however I often get a large error associated with the S value (sample length), even when my GOF is decent (<1.45). Do any of you know why this would happen? 6. Should I refine the “Scale” or scale factor. (Currently I do) 7. IMPORTANT: Originally I was refining the crystallite size but it always refined to a very small value (~300nm), where as NIST claims 660 LAB6 should have a mean grain size of a few microns or more. I assume this happens because the TOPAS is accounting for instrument caused peak broadening by making the crystallite size smaller than it actually is in the software. However, when I do refine the grain size I do get a better fit. Should I leave this unchecked, refine it, or fix it at a reasonable value of ~2500 nm. In summary, currently I am only refining the Lorentz HW and “Area” in the emission profile, zero shift error, the Finger parameters (S & H), the scale factor, and nothing else. I am unsure if I should be refining anything else such as the crystallite size, tube tails and other forms of equatorial convergence, or if there is something else that is important which I am disregarding completely. I am also unsure if I am correct in refining Lorentz HW and area in the emission profile. Sorry if I got a little long winded; I just wanted to give enough detail so people could answer. Thank you in advance for your help. Patrick James P. Cline Ceramics Division National Institute of Standards and Technology 100 Bureau Dr. stop 8520 [ B113 / Bldg 217 ] Gaithersburg, MD 20899-8523USA jcl...@nist.gov (301) 975 5793 FAX (301) 975 5334
Rietveld refinement in TOPAS with parallel beam geometry
Since this is my first post I will start with a brief introduction. My name is Patrick Price and I am in my second year of graduate school. My thesis work involves the investigation of phase equilibria in perovskites. I am using a Bruker D8 Discover diffractometer with parallel beam geometry. The diffractometer has a Cu K-alpha X-Ray source with a Si Gobel mirror and a Ge monochromator giving a parallel beam monochromatic x-ray source. The receiving side has Soller slits and a Tl-doped NaI point detector. I am trying to teach myself how to use TOPAS to PROPERLY analyze my data using Rietveld refinement techniques. I have recently taken a scan of the NIST line profile 660 LaB6 standard followed by scans of my perovskite powders using a step size of 0.02 degrees and scan time of 4 seconds. Most of the articles I have read are specific to convergent/divergent beam geometries and I do not know how much of that information transfers to parallel beam geometries. If anyone could help me answer the following questions I would greatly appreciate it. These questions mainly address which parameters should be refined with the LaB6 standard when using parallel beam geometry. 1. I need to use the scan of the LaB6 powders to characterize the contributions of the instrument to the diffraction profile. Starting with the emission profile, TOPAS asks for the wavelength, the Area, and the Lorentz Half Width. First, I assume the wavelength I should be the more recent Cu Ka wavelength of 0.154059 nm instead of 0.154056 nm. Second, does Cu Ka have a definite Lorentz HW and “Area” or should these parameters be refined with the LaB6 diffraction pattern? 2. Since I have a Ge monochromater I assume the Lorentz polarization factor should be fixed at 27.3 (Is this correct?). Obviously the lattice parameters and atomic positions would be fixed. 3. I read that you should NOT refine both the zero shift error and sample displacement, and since it is parallel beam I only refine the zero shift error. Should I refine surface roughness, absorption, or sample tilt with the LaB6? (Currently I do not refine these) 4. Am I correct in assuming that I do not have any EQUITORIAL convolutions (e.g. from slits, FDS, beam spill, VDS) since it is parallel beam geometry? What about TUBE TAILS? 5. I am using the Finger_et_al method to refine the AXIAL convolutions, however I often get a large error associated with the S value (sample length), even when my GOF is decent (<1.45). Do any of you know why this would happen? 6. Should I refine the “Scale” or scale factor. (Currently I do) 7. IMPORTANT: Originally I was refining the crystallite size but it always refined to a very small value (~300nm), where as NIST claims 660 LAB6 should have a mean grain size of a few microns or more. I assume this happens because the TOPAS is accounting for instrument caused peak broadening by making the crystallite size smaller than it actually is in the software. However, when I do refine the grain size I do get a better fit. Should I leave this unchecked, refine it, or fix it at a reasonable value of ~2500 nm. In summary, currently I am only refining the Lorentz HW and “Area” in the emission profile, zero shift error, the Finger parameters (S & H), the scale factor, and nothing else. I am unsure if I should be refining anything else such as the crystallite size, tube tails and other forms of equatorial convergence, or if there is something else that is important which I am disregarding completely. I am also unsure if I am correct in refining Lorentz HW and area in the emission profile. Sorry if I got a little long winded; I just wanted to give enough detail so people could answer. Thank you in advance for your help. Patrick
Powder Diffraction & Rietveld Refinement School 2010
Dear All, The EPSRC/IUCr/PCG-SCMP supported biennial Powder Diffraction and Rietveld Refinement School will take place at Durham University, 18th - 22nd April 2010. The course will offer a combination of lectures covering the theoretical aspects of powder diffraction and Rietveld refinement, problem sessions/tutorials and extensive hands-on practical sessions using a variety of modern software packages. Topics to be covered will include: * Data collection strategies for X-ray and neutron diffraction * Constant wavelength and time of flight diffraction * Modelling peak shapes * Indexing powder patterns * Rietveld, Le Bail and Pawley fitting methods * X-ray and neutron combined Rietveld refinement * Restrained refinements * Rigid body refinements Examples and tutorials will cover both extended and molecular systems. Lectures will be given by Prof. John Evans, Dr. Ivana Evans, Dr. Jeremy Cockroft and Prof. Andy Fitch. Student bursaries will be available to contribute to local costs or travel expenses of applicants from UK academic institutions. We will also offer a number of IUCr bursaries to overseas students. For further information and informal inquiries about the School please contact Ivana Evans (ivana.radosavlje...@durham.ac.uk). Online applications can be submitted until 31st December 2009, at the Powder Diffraction and Rietveld Refinement School 2010 website: http://www.dur.ac.uk/john.evans/webpages/pcg_rietveld_school_2010.htm Ivana Evans Dr. Ivana Radosavljevic Evans Lecturer in Structural/Materials Chemistry Department of Chemistry Durham University Durham DH1 3LE, U.K. Office: CG 244 Phone: (0191) 334-2594 Fax: (0191) 384-4737
Re: LP factor in the Rietveld refinement
Thanks, Nicolae, for the didactic comment, but I must add that the expression pol = SIN(PSI)**2 + COS(PSI)**2*COS(2*TET1)**2*COS(2*TET2)**2 *.*COS(2*TETm)**2*COS(2*TETb)**2 is an idealization and the real polarization factor may deviate notably from the idealized one depending on the crystal type (perfection/mosaicity) and other factors especially for multi-bounce systems. So, regarding the polarization factor of a real system in use, it is better to either consult the manufacturer or try determining it experimentally, for example, by measuring the same standard sample with and without monochromator. Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660049, K. Marx 42, Krasnoyarsk , Russia www.icct.ru/eng/content/persons/Sol_LA www.geocities.com/l_solovyov *** --- On Mon, 7/27/09, Nicolae Popa wrote: > From: Nicolae Popa > Subject: Re: LP factor in the Rietveld refinement > To: "Leonid Solovyov" , rietveld_l@ill.fr > Date: Monday, July 27, 2009, 11:04 AM > Right, but specially for students- > beginners we must be much, let say, didactic > > LP means (Lorentz) * (Polarisation) > What is important in Rietveld refinement when a lot of > mirrors & monochromators are present is how they change > (Polarization) > because (Lorentz) is changed by adding factors independent > on hkl, then entering in the scaling factor > > Presuming the same scattering plane for all "scatterers" > the polarization factor is: > > > pol = SIN(PSI)**2 + > COS(PSI)**2*COS(2*TET1)**2*COS(2*TET2)**2 > *.*COS(2*TETm)**2*COS(2*TETb)**2 > > > where TET1, TET2, ., > TETm are the Bragg angles at monochromator > 1, 2, ,m > > and where TETb is the Bragg angle at > sample (depending on hkl) > > and where PSI is the angle between polarization > vector of the incident beam - IF it is TOTALLY POLARIZED!!! > - and the scattering plane; > > If the incident beam is NOT POLARIZED the averages of both > SIN(PSI)**2 and COS(PSI)**2 result in 1/2. > > If the incident beam is partially polarized one replace for > example SIN(PSI)**2 by P0 , consequently > COS(PSI)**2 = 1 - P0 and one refine P0 > > If the geometry is much complicated (different scattering > planes for different monochromators) "pol" should be > calculated for the given > > geometry by applying successively the known formula > (see a book of electrodynamics, e.g.. Landau) > > Ej+1 = (Ej X u)Xu and taking at the END: > |E(last)|**2 / |E0|**2 (X means > vectorial product) > > where Ej is the electric field vector in the beam scattered > j times and u is the unit vector along the scattered > beam j+1 > > Best wishes, > > Nicolae Popa > >
Re: LP factor in the Rietveld refinement
Right, but specially for students- beginners we must be much, let say, didactic LP means (Lorentz) * (Polarisation) What is important in Rietveld refinement when a lot of mirrors & monochromators are present is how they change (Polarization) because (Lorentz) is changed by adding factors independent on hkl, then entering in the scaling factor Presuming the same scattering plane for all "scatterers" the polarization factor is: pol = SIN(PSI)**2 + COS(PSI)**2*COS(2*TET1)**2*COS(2*TET2)**2 *.*COS(2*TETm)**2*COS(2*TETb)**2 where TET1, TET2, ., TETm are the Bragg angles at monochromator 1, 2, ,m and where TETb is the Bragg angle at sample (depending on hkl) and where PSI is the angle between polarization vector of the incident beam - IF it is TOTALLY POLARIZED!!! - and the scattering plane; If the incident beam is NOT POLARIZED the averages of both SIN(PSI)**2 and COS(PSI)**2 result in 1/2. If the incident beam is partially polarized one replace for example SIN(PSI)**2 by P0 , consequently COS(PSI)**2 = 1 - P0 and one refine P0 If the geometry is much complicated (different scattering planes for different monochromators) "pol" should be calculated for the given geometry by applying successively the known formula (see a book of electrodynamics, e.g.. Landau) Ej+1 = (Ej X u)Xu and taking at the END: |E(last)|**2 / |E0|**2 (X means vectorial product) where Ej is the electric field vector in the beam scattered j times and u is the unit vector along the scattered beam j+1 Best wishes, Nicolae Popa - Original Message - From: "Leonid Solovyov" To: Sent: Sunday, July 26, 2009 9:05 AM Subject: RE: LP factor in the Rietveld refinement In principle, the LP correction for a multi-bounce monochromator is similar to that for a single-crystal one with the same crystal type and reflection indexes (or diffraction angle). The exact LP value depends, as well, on the crystal perfection (mosaicity) and for supremely precise measurements one might consider refining the LP value as was mentioned by Kurt and Peter. Besides the angular range, the correlation with thermal parameters, and the instrument alignment, one more problem of the LP refinement is the correct choice of the atomic scattering curves in accordance with the oxidation states which might be not quite obvious in general. Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660049, K. Marx 42, Krasnoyarsk , Russia www.icct.ru/eng/content/persons/Sol_LA www.geocities.com/l_solovyov *** --- On Sun, 7/26/09, Peter Y. Zavalij wrote: From: Peter Y. Zavalij Subject: RE: LP factor in the Rietveld refinement To: rietveld_l@ill.fr Date: Sunday, July 26, 2009, 5:03 AM That's right. LP refinement works just fine within TOPAS but angular range as wide as possible is needed. If it is up to 140-150 deg. 2thteta LP does not correlate much with thermal parameters. Refined LP is not exact but very close. Peter Zavalij X-ray Crystallographic Center University of Maryland College Park, MD Office: (301)405-1861 Lab: (301)405-3230 Fax: (301)314-9121 -Original Message- From: Kurt Leinenweber [mailto:ku...@asu.edu] Sent: Saturday, July 25, 2009 8:53 PM To: alor...@unex.es; Leonid Solovyov Cc: rietveld_l@ill.fr Subject: RE: LP factor in the Rietveld refinement Hi all, I haven't actually DONE this, so maybe I shouldn't put my 2 cents in, but can't you refine the polarization factor by using a standard such as Y2O3 and fixing the structure and thermal parameters of the standard while refining the polarization angle? The angle so obtained should agree with what the theory tells you for your diffractometer configuration, but it seems more comforting to verify it by a measurement. - Kurt From: alor...@unex.es [mailto:alor...@unex.es] Sent: Sat 7/25/2009 1:29 PM To: Leonid Solovyov Cc: rietveld_l@ill.fr Subject: Re: LP factor in the Rietveld refinement In this context: What about the LP for a Goebel mirror followed by a 4-bounce or 2-bounce primary monochromator? Best regards angel l. ortiz __ NOD32 4280 (20090726) Information __ This message was checked by NOD32 antivirus system. http://www.eset.com
RE: LP factor in the Rietveld refinement
In principle, the LP correction for a multi-bounce monochromator is similar to that for a single-crystal one with the same crystal type and reflection indexes (or diffraction angle). The exact LP value depends, as well, on the crystal perfection (mosaicity) and for supremely precise measurements one might consider refining the LP value as was mentioned by Kurt and Peter. Besides the angular range, the correlation with thermal parameters, and the instrument alignment, one more problem of the LP refinement is the correct choice of the atomic scattering curves in accordance with the oxidation states which might be not quite obvious in general. Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660049, K. Marx 42, Krasnoyarsk , Russia www.icct.ru/eng/content/persons/Sol_LA www.geocities.com/l_solovyov *** --- On Sun, 7/26/09, Peter Y. Zavalij wrote: > From: Peter Y. Zavalij > Subject: RE: LP factor in the Rietveld refinement > To: rietveld_l@ill.fr > Date: Sunday, July 26, 2009, 5:03 AM > That's right. LP refinement works > just fine within TOPAS but angular range > as wide as possible is needed. If it is up to 140-150 deg. > 2thteta LP does > not correlate much with thermal parameters. Refined LP is > not exact but very > close. > > Peter Zavalij > > X-ray Crystallographic Center > University of Maryland > College Park, MD > > Office: (301)405-1861 > Lab: (301)405-3230 > Fax: (301)314-9121 > > > > > -Original Message- > From: Kurt Leinenweber [mailto:ku...@asu.edu] > Sent: Saturday, July 25, 2009 8:53 PM > To: alor...@unex.es; > Leonid Solovyov > Cc: rietveld_l@ill.fr > Subject: RE: LP factor in the Rietveld refinement > > Hi all, > > I haven't actually DONE this, so maybe I shouldn't put my 2 > cents in, but > can't you refine the polarization factor by using a > standard such as Y2O3 > and fixing the structure and thermal parameters of the > standard while > refining the polarization angle? > > The angle so obtained should agree with what the theory > tells you for your > diffractometer configuration, but it seems more comforting > to verify it by a > measurement. > > - Kurt > > ____ > > From: alor...@unex.es > [mailto:alor...@unex.es] > Sent: Sat 7/25/2009 1:29 PM > To: Leonid Solovyov > Cc: rietveld_l@ill.fr > Subject: Re: LP factor in the Rietveld refinement > > > > In this context: > > What about the LP for a Goebel mirror followed by a > 4-bounce or 2-bounce > primary monochromator? > > Best regards > > angel l. ortiz >
RE: LP factor in the Rietveld refinement
That's right. LP refinement works just fine within TOPAS but angular range as wide as possible is needed. If it is up to 140-150 deg. 2thteta LP does not correlate much with thermal parameters. Refined LP is not exact but very close. Peter Zavalij X-ray Crystallographic Center University of Maryland College Park, MD Office: (301)405-1861 Lab: (301)405-3230 Fax: (301)314-9121 -Original Message- From: Kurt Leinenweber [mailto:ku...@asu.edu] Sent: Saturday, July 25, 2009 8:53 PM To: alor...@unex.es; Leonid Solovyov Cc: rietveld_l@ill.fr Subject: RE: LP factor in the Rietveld refinement Hi all, I haven't actually DONE this, so maybe I shouldn't put my 2 cents in, but can't you refine the polarization factor by using a standard such as Y2O3 and fixing the structure and thermal parameters of the standard while refining the polarization angle? The angle so obtained should agree with what the theory tells you for your diffractometer configuration, but it seems more comforting to verify it by a measurement. - Kurt From: alor...@unex.es [mailto:alor...@unex.es] Sent: Sat 7/25/2009 1:29 PM To: Leonid Solovyov Cc: rietveld_l@ill.fr Subject: Re: LP factor in the Rietveld refinement In this context: What about the LP for a Goebel mirror followed by a 4-bounce or 2-bounce primary monochromator? Best regards angel l. ortiz > > As far as I know, for X-ray mirrors the LP angle is near zero. > > Leonid > > *** > Leonid A. Solovyov > Institute of Chemistry and Chemical Technology > 660049, K. Marx 42, Krasnoyarsk , Russia > www.icct.ru/eng/content/persons/Sol_LA > www.geocities.com/l_solovyov > *** > > --- On Sat, 7/25/09, chu...@hkusua.hku.hk wrote: > >> From: chu...@hkusua.hku.hk >> Subject: Re: LP factor in the Rietveld refinement >> To: "Ross H Colman" >> Cc: rietveld_l@ill.fr >> Date: Saturday, July 25, 2009, 4:16 AM >> Dear Ross, >> >> How about the LP factor/monochromator angle if using Gobel >> mirror in >> my D8 system? >> >> Thanks! >> >> stephen >> > > > > > No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.392 / Virus Database: 270.13.30/2262 - Release Date: 07/25/09 18:01:00
RE: LP factor in the Rietveld refinement
Hi all, I haven't actually DONE this, so maybe I shouldn't put my 2 cents in, but can't you refine the polarization factor by using a standard such as Y2O3 and fixing the structure and thermal parameters of the standard while refining the polarization angle? The angle so obtained should agree with what the theory tells you for your diffractometer configuration, but it seems more comforting to verify it by a measurement. - Kurt From: alor...@unex.es [mailto:alor...@unex.es] Sent: Sat 7/25/2009 1:29 PM To: Leonid Solovyov Cc: rietveld_l@ill.fr Subject: Re: LP factor in the Rietveld refinement In this context: What about the LP for a Goebel mirror followed by a 4-bounce or 2-bounce primary monochromator? Best regards angel l. ortiz > > As far as I know, for X-ray mirrors the LP angle is near zero. > > Leonid > > *** > Leonid A. Solovyov > Institute of Chemistry and Chemical Technology > 660049, K. Marx 42, Krasnoyarsk , Russia > www.icct.ru/eng/content/persons/Sol_LA > www.geocities.com/l_solovyov > *** > > --- On Sat, 7/25/09, chu...@hkusua.hku.hk wrote: > >> From: chu...@hkusua.hku.hk >> Subject: Re: LP factor in the Rietveld refinement >> To: "Ross H Colman" >> Cc: rietveld_l@ill.fr >> Date: Saturday, July 25, 2009, 4:16 AM >> Dear Ross, >> >> How about the LP factor/monochromator angle if using Gobel >> mirror in >> my D8 system? >> >> Thanks! >> >> stephen >> > > > > >
Re: LP factor in the Rietveld refinement
In this context: What about the LP for a Goebel mirror followed by a 4-bounce or 2-bounce primary monochromator? Best regards angel l. ortiz > > As far as I know, for X-ray mirrors the LP angle is near zero. > > Leonid > > *** > Leonid A. Solovyov > Institute of Chemistry and Chemical Technology > 660049, K. Marx 42, Krasnoyarsk , Russia > www.icct.ru/eng/content/persons/Sol_LA > www.geocities.com/l_solovyov > *** > > --- On Sat, 7/25/09, chu...@hkusua.hku.hk wrote: > >> From: chu...@hkusua.hku.hk >> Subject: Re: LP factor in the Rietveld refinement >> To: "Ross H Colman" >> Cc: rietveld_l@ill.fr >> Date: Saturday, July 25, 2009, 4:16 AM >> Dear Ross, >> >> How about the LP factor/monochromator angle if using Gobel >> mirror in >> my D8 system? >> >> Thanks! >> >> stephen >> > > > > >
Re: LP factor in the Rietveld refinement
As far as I know, for X-ray mirrors the LP angle is near zero. Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660049, K. Marx 42, Krasnoyarsk , Russia www.icct.ru/eng/content/persons/Sol_LA www.geocities.com/l_solovyov *** --- On Sat, 7/25/09, chu...@hkusua.hku.hk wrote: > From: chu...@hkusua.hku.hk > Subject: Re: LP factor in the Rietveld refinement > To: "Ross H Colman" > Cc: rietveld_l@ill.fr > Date: Saturday, July 25, 2009, 4:16 AM > Dear Ross, > > How about the LP factor/monochromator angle if using Gobel > mirror in > my D8 system? > > Thanks! > > stephen >
Re: LP factor in the Rietveld refinement
Dear Ross, How about the LP factor/monochromator angle if using Gobel mirror in my D8 system? Thanks! stephen - Message from ucca...@ucl.ac.uk - Date: Thu, 23 Jul 2009 09:52:55 +0100 From: Ross H Colman Reply-To: Ross H Colman Subject: Re: LP factor in the Rietveld refinement To: rietveld_l@ill.fr Dear all, Just to be complete, the Topas technical reference manual also gives the LP values for a few other common monchromators: Pg109 "Values for most common monochromators (Cu radiation) are: Ge : 27.3 Graphite : 26.4 Quartz : 26.6" Regards Ross Colman Ross Colman G19 Christopher Ingold Laboratories University College London Department of Chemistry 20 Gordon Street London WC1H 0AJ Phone: +44 (0)20 7679 4636 Internal: 24636 Email: ross.col...@ucl.ac.uk - End message from ucca...@ucl.ac.uk -
Re: AW: LP factor in the Rietveld refinement
The surface roughness effect depends on both the roughness and the absorption coefficient, and for LaB6 it may be notable if the sample surface is really rough. However, this effect leads to a systematic DECREASE of the LOW-ANGLE reflections which seems to be not the case since the correction with LP=90 works conversely. Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660049, K. Marx 42, Krasnoyarsk , Russia www.icct.ru/eng/content/persons/Sol_LA www.geocities.com/l_solovyov *** --- On Thu, 7/23/09, David Lee wrote: > From: David Lee > Subject: Re: AW: LP factor in the Rietveld refinement > To: "Reitveld" > Date: Thursday, July 23, 2009, 2:19 PM > I have a question about the surface > roughness. The LaB6 powders that I have seen > are > very finely ground and produce very flat, smooth > samples. Is the roughness connected > with the absorption? I'm thinking along > the lines that a low absorbing, rough sample > might not "look" as rough to an x-ray beam as a high > absorbing, smoother sample. > > Thanks, > > David Lee, Ph.D. > DTLee Scientific, llc > http://www.dtlee.com > 614-562-6230 > > On Jul 23, 2009, at 5:23 AM, Hinrichsen, Bernd wrote: > > > One intensity correction that is perhaps more > realistic is surface roughness. This does have a vaguely > similar angular dependence to the LP correction. This > correction is generally only applied to highly absorbing > samples in Bragg-Brentano (or generally reflection) setups. > This would seem to be the case for the LaB6 measurement > mentioned by Peter. > > > > Greetings > > Bernd > > > > > > -Ursprüngliche Nachricht- > > Von: Peter Y. Zavalij [mailto:pzava...@umd.edu] > > Gesendet: Donnerstag, 23. Juli 2009 05:52 > > An: rietveld_l@ill.fr > > Betreff: RE: LP factor in the Rietveld refinement > > > > Well... the situation with LP is not so simple. Using > TOPAS for refinement > > data collected on D8 advance with Ni-filter and > LynxEye detector I observe > > the following: > > - For all samples LP=0 is OK and gives the best fit as > it should be by the > > book. > > - HOWEVER for LaB6 standard LP=0 yields very poor fit > for several high angle > > reflections (>120 deg. 2theta) while LP=90 gives > perfect fit. The difference > > in R factors 12% and 4% cannot be simply ignored... > > > > Can anyone explain this? > > > > > > Peter Zavalij > > > > X-ray Crystallographic Center > > University of Maryland > > College Park, MD > > > > Office: (301)405-1861 > > Lab: (301)405-3230 > > Fax: (301)314-9121 > >
Re: AW: LP factor in the Rietveld refinement
I have a question about the surface roughness.The LaB6 powders that I have seen are very finely ground and produce very flat, smooth samples. Is the roughness connected with the absorption? I'm thinking along the lines that a low absorbing, rough sample might not "look" as rough to an x-ray beam as a high absorbing, smoother sample. Thanks, David Lee, Ph.D. DTLee Scientific, llc http://www.dtlee.com 614-562-6230 On Jul 23, 2009, at 5:23 AM, Hinrichsen, Bernd wrote: One intensity correction that is perhaps more realistic is surface roughness. This does have a vaguely similar angular dependence to the LP correction. This correction is generally only applied to highly absorbing samples in Bragg-Brentano (or generally reflection) setups. This would seem to be the case for the LaB6 measurement mentioned by Peter. Greetings Bernd -Ursprüngliche Nachricht- Von: Peter Y. Zavalij [mailto:pzava...@umd.edu] Gesendet: Donnerstag, 23. Juli 2009 05:52 An: rietveld_l@ill.fr Betreff: RE: LP factor in the Rietveld refinement Well... the situation with LP is not so simple. Using TOPAS for refinement data collected on D8 advance with Ni-filter and LynxEye detector I observe the following: - For all samples LP=0 is OK and gives the best fit as it should be by the book. - HOWEVER for LaB6 standard LP=0 yields very poor fit for several high angle reflections (>120 deg. 2theta) while LP=90 gives perfect fit. The difference in R factors 12% and 4% cannot be simply ignored... Can anyone explain this? Peter Zavalij X-ray Crystallographic Center University of Maryland College Park, MD Office: (301)405-1861 Lab: (301)405-3230 Fax: (301)314-9121 -Original Message- From: Ross Williams [mailto:ross.willi...@curtin.edu.au] Sent: Wednesday, July 22, 2009 8:43 PM To: Jon Wright; xiu...@ualberta.ca Cc: rietveld_l@ill.fr Subject: RE: LP factor in the Rietveld refinement Hi Xiujun, Jon is correct, but to answer your question fully, the angle is used in an equation to scale the peaks as function of 2theta. If you look in the Technical Reference Manual of TOPAS states that the LP factor (for x-rays) is given by LP = (1 + cos(2th)^2 cos(2th_m)^2) / (cos(theta) sun(theta)^2) 2th_m is the angle mentioned by Jon, ie 26.4° when using Cu Kalpha with a graphic monochromator, 0° when using unpolarised beam, and 90° for full polarised. Or in TOPAS macro language : scale_pks = (1 + Cos(CeV(c,v) Deg)^2 Cos(2 Th)^2) /(Sin(Th)^2 Cos(Th)); The Technical Reference has a derivation of the LP equation above and compares it to parameters used in GSAS and Fullprof. Kind Regards, Ross + Ross Williams PhD Student Centre for Materials Research Department of Imaging and Applied Physics Curtin University of Technology GPO Box U1987 Perth WA 6845 Western Australia Phone: +61 (0)8 9266 4219 Fax: +61 (0)8 9266 2377 Email: ross.willi...@curtin.edu.au -Original Message- From: Jon Wright [mailto:wri...@esrf.fr] Sent: Thursday, 23 July 2009 5:26 AM To: xiu...@ualberta.ca Cc: rietveld_l@ill.fr Subject: Re: LP factor in the Rietveld refinement Sounds like the parameter is the monochromator angle you would need to use to convert an unpolarised beam into a beam with the polarisation state you have (eg, 90 degrees gives 100% polarised). Don't confuse this with the actual monochromator angle at the synchrotron, as the bean is usually polarised before it reaches the monochromator anyway. With some packages you can set the monochromator "roll" angle to put the polarisation in the right plane, depending which way up an area detector was mounted. Good luck, Jon xiu...@ualberta.ca wrote: Hello, everyone, I have some questions about the refinement in Topas. When we put the instrument parameters, we always include the LP factor, and set it to a constant value. I thought LP factor is a function of theta and not a constant value, so my question is what exact the constant value means. Why for unpolarized radiation, it is equal to 0, and for synchrotron radiation it is equal to 90. Sorry to throw so many questions. Thank a lot for any help. Xiujun Li Master Student Advanced Materials and Processing Laboratory Chemical and Materials Engineering University of Alberta Edmonton, Alberta, Canada T6G 2G6 Phone: 1-780-492-0701 No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.392 / Virus Database: 270.13.24/2255 - Release Date: 07/22/09 18:00:00 Bruker AXS GmbH, Karlsruhe HRB 107524 Amtsgericht Mannheim, Umsatzsteuer-Ident.Nr. DE812037551, Geschäftsführer - Dr. Frank Burgäzy, Bernard Kolodziej, Stephan Franz Westermann Der Inhalt dieser E-Mail ist vertraulich und ausschliesslich f
AW: LP factor in the Rietveld refinement
One intensity correction that is perhaps more realistic is surface roughness. This does have a vaguely similar angular dependence to the LP correction. This correction is generally only applied to highly absorbing samples in Bragg-Brentano (or generally reflection) setups. This would seem to be the case for the LaB6 measurement mentioned by Peter. Greetings Bernd -Ursprüngliche Nachricht- Von: Peter Y. Zavalij [mailto:pzava...@umd.edu] Gesendet: Donnerstag, 23. Juli 2009 05:52 An: rietveld_l@ill.fr Betreff: RE: LP factor in the Rietveld refinement Well... the situation with LP is not so simple. Using TOPAS for refinement data collected on D8 advance with Ni-filter and LynxEye detector I observe the following: - For all samples LP=0 is OK and gives the best fit as it should be by the book. - HOWEVER for LaB6 standard LP=0 yields very poor fit for several high angle reflections (>120 deg. 2theta) while LP=90 gives perfect fit. The difference in R factors 12% and 4% cannot be simply ignored... Can anyone explain this? Peter Zavalij X-ray Crystallographic Center University of Maryland College Park, MD Office: (301)405-1861 Lab: (301)405-3230 Fax: (301)314-9121 -Original Message- From: Ross Williams [mailto:ross.willi...@curtin.edu.au] Sent: Wednesday, July 22, 2009 8:43 PM To: Jon Wright; xiu...@ualberta.ca Cc: rietveld_l@ill.fr Subject: RE: LP factor in the Rietveld refinement Hi Xiujun, Jon is correct, but to answer your question fully, the angle is used in an equation to scale the peaks as function of 2theta. If you look in the Technical Reference Manual of TOPAS states that the LP factor (for x-rays) is given by LP = (1 + cos(2th)^2 cos(2th_m)^2) / (cos(theta) sun(theta)^2) 2th_m is the angle mentioned by Jon, ie 26.4° when using Cu Kalpha with a graphic monochromator, 0° when using unpolarised beam, and 90° for full polarised. Or in TOPAS macro language : scale_pks = (1 + Cos(CeV(c,v) Deg)^2 Cos(2 Th)^2) /(Sin(Th)^2 Cos(Th)); The Technical Reference has a derivation of the LP equation above and compares it to parameters used in GSAS and Fullprof. Kind Regards, Ross + Ross Williams PhD Student Centre for Materials Research Department of Imaging and Applied Physics Curtin University of Technology GPO Box U1987 Perth WA 6845 Western Australia Phone: +61 (0)8 9266 4219 Fax: +61 (0)8 9266 2377 Email: ross.willi...@curtin.edu.au -Original Message- From: Jon Wright [mailto:wri...@esrf.fr] Sent: Thursday, 23 July 2009 5:26 AM To: xiu...@ualberta.ca Cc: rietveld_l@ill.fr Subject: Re: LP factor in the Rietveld refinement Sounds like the parameter is the monochromator angle you would need to use to convert an unpolarised beam into a beam with the polarisation state you have (eg, 90 degrees gives 100% polarised). Don't confuse this with the actual monochromator angle at the synchrotron, as the bean is usually polarised before it reaches the monochromator anyway. With some packages you can set the monochromator "roll" angle to put the polarisation in the right plane, depending which way up an area detector was mounted. Good luck, Jon xiu...@ualberta.ca wrote: > Hello, everyone, > > I have some questions about the refinement in Topas. > > When we put the instrument parameters, we always include the LP > factor, and set it to a constant value. I thought LP factor is a > function of theta and not a constant value, so my question is what > exact the constant value means. Why for unpolarized radiation, it is > equal to 0, and for synchrotron radiation it is equal to 90. Sorry to > throw so many questions. > > Thank a lot for any help. > > Xiujun Li > Master Student > Advanced Materials and Processing Laboratory > Chemical and Materials Engineering > University of Alberta > Edmonton, Alberta, Canada T6G 2G6 > Phone: 1-780-492-0701 > No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.392 / Virus Database: 270.13.24/2255 - Release Date: 07/22/09 18:00:00 Bruker AXS GmbH, Karlsruhe HRB 107524 Amtsgericht Mannheim, Umsatzsteuer-Ident.Nr. DE812037551, Geschäftsführer - Dr. Frank Burgäzy, Bernard Kolodziej, Stephan Franz Westermann Der Inhalt dieser E-Mail ist vertraulich und ausschliesslich fuer den bezeichneten Adressaten bestimmt. Wenn Sie nicht der vorgesehene Adressat dieser E-Mail oder dessen Vertreter sein sollten, so beachten Sie bitte, dass jede Form der Kenntnisnahme, Veroeffentlichung, Vervielfaeltigung oder Weitergabe des Inhalts dieser E-Mail unzulaessig ist. Wir bitten Sie, sich in diesem Fall mit dem Absender der E-Mail in Verbindung zu setzen. The information contained in this email is confidential. It is intended solely fo
Re: LP factor in the Rietveld refinement
Dear all, Just to be complete, the Topas technical reference manual also gives the LP values for a few other common monchromators: Pg109 "Values for most common monochromators (Cu radiation) are: Ge : 27.3 Graphite : 26.4 Quartz : 26.6" Regards Ross Colman Ross Colman G19 Christopher Ingold Laboratories University College London Department of Chemistry 20 Gordon Street London WC1H 0AJ Phone: +44 (0)20 7679 4636 Internal: 24636 Email: ross.col...@ucl.ac.uk
RE: LP factor in the Rietveld refinement
Dear Angel, In general, the LP correction angle is the diffraction angle (2theta) of the monochromator crystal. If the primary monochromator is Si(111) then the angle is 28.44 for CuK_alpha1. Best regards, Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660049, K. Marx 42, Krasnoyarsk , Russia www.icct.ru/eng/content/persons/Sol_LA www.geocities.com/l_solovyov *** --- On Thu, 7/23/09, alor...@unex.es wrote: > From: alor...@unex.es > Subject: RE: LP factor in the Rietveld refinement > To: "Leonid Solovyov" > Cc: rietveld_l@ill.fr > Date: Thursday, July 23, 2009, 7:00 AM > Dear All, > > In this scenario, which should be the number for LP in > Topas if ones has a > D8 with a primary monochromator for pure CuKalpha1? > > thanks for the response, > > angel l. ortiz >
RE: LP factor in the Rietveld refinement
Dear All, In this scenario, which should be the number for LP in Topas if ones has a D8 with a primary monochromator for pure CuKalpha1? thanks for the response, angel l. ortiz > > Dear Peter, > > Of course the LP correction can't be sample-dependent and for your > configuration LP=0 should be Ok for all samples. It seems that you have an > intensity loss at high-angles that may be partly compensated by LP=90. > Possible reason may be in a misalignment of the anti-scattering slits or > screen (knife) if you use them. > > Best regards, > Leonid > > *** > Leonid A. Solovyov > Institute of Chemistry and Chemical Technology > 660049, K. Marx 42, Krasnoyarsk , Russia > www.icct.ru/eng/content/persons/Sol_LA > www.geocities.com/l_solovyov > *** > > --- On Thu, 7/23/09, Peter Y. Zavalij wrote: > > From: Peter Y. Zavalij > Subject: RE: LP factor in the Rietveld refinement > To: rietveld_l@ill.fr > Date: Thursday, July 23, 2009, 4:52 AM > > Well... the situation with LP is not so simple. Using TOPAS for refinement > data collected on D8 advance with Ni-filter and LynxEye detector I observe > the following: > - For all samples LP=0 is OK and gives the best fit as it should be by the > book. > - HOWEVER for LaB6 standard LP=0 yields very poor fit for several high > angle > reflections (>120 deg. 2theta) while LP=90 gives perfect fit. The > difference > in R factors 12% and 4% cannot be simply ignored... > > Can anyone explain this? > > > Peter Zavalij > > X-ray Crystallographic Center > University of Maryland > College Park, MD > > Office: (301)405-1861 > Lab: (301)405-3230 > Fax: (301)314-9121 > > > > >
RE: LP factor in the Rietveld refinement
Dear Peter, Of course the LP correction can't be sample-dependent and for your configuration LP=0 should be Ok for all samples. It seems that you have an intensity loss at high-angles that may be partly compensated by LP=90. Possible reason may be in a misalignment of the anti-scattering slits or screen (knife) if you use them. Best regards, Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660049, K. Marx 42, Krasnoyarsk , Russia www.icct.ru/eng/content/persons/Sol_LA www.geocities.com/l_solovyov *** --- On Thu, 7/23/09, Peter Y. Zavalij wrote: From: Peter Y. Zavalij Subject: RE: LP factor in the Rietveld refinement To: rietveld_l@ill.fr Date: Thursday, July 23, 2009, 4:52 AM Well... the situation with LP is not so simple. Using TOPAS for refinement data collected on D8 advance with Ni-filter and LynxEye detector I observe the following: - For all samples LP=0 is OK and gives the best fit as it should be by the book. - HOWEVER for LaB6 standard LP=0 yields very poor fit for several high angle reflections (>120 deg. 2theta) while LP=90 gives perfect fit. The difference in R factors 12% and 4% cannot be simply ignored... Can anyone explain this? Peter Zavalij X-ray Crystallographic Center University of Maryland College Park, MD Office: (301)405-1861 Lab: (301)405-3230 Fax: (301)314-9121
RE: LP factor in the Rietveld refinement
Well... the situation with LP is not so simple. Using TOPAS for refinement data collected on D8 advance with Ni-filter and LynxEye detector I observe the following: - For all samples LP=0 is OK and gives the best fit as it should be by the book. - HOWEVER for LaB6 standard LP=0 yields very poor fit for several high angle reflections (>120 deg. 2theta) while LP=90 gives perfect fit. The difference in R factors 12% and 4% cannot be simply ignored... Can anyone explain this? Peter Zavalij X-ray Crystallographic Center University of Maryland College Park, MD Office: (301)405-1861 Lab: (301)405-3230 Fax: (301)314-9121 -Original Message- From: Ross Williams [mailto:ross.willi...@curtin.edu.au] Sent: Wednesday, July 22, 2009 8:43 PM To: Jon Wright; xiu...@ualberta.ca Cc: rietveld_l@ill.fr Subject: RE: LP factor in the Rietveld refinement Hi Xiujun, Jon is correct, but to answer your question fully, the angle is used in an equation to scale the peaks as function of 2theta. If you look in the Technical Reference Manual of TOPAS states that the LP factor (for x-rays) is given by LP = (1 + cos(2th)^2 cos(2th_m)^2) / (cos(theta) sun(theta)^2) 2th_m is the angle mentioned by Jon, ie 26.4° when using Cu Kalpha with a graphic monochromator, 0° when using unpolarised beam, and 90° for full polarised. Or in TOPAS macro language : scale_pks = (1 + Cos(CeV(c,v) Deg)^2 Cos(2 Th)^2) /(Sin(Th)^2 Cos(Th)); The Technical Reference has a derivation of the LP equation above and compares it to parameters used in GSAS and Fullprof. Kind Regards, Ross + Ross Williams PhD Student Centre for Materials Research Department of Imaging and Applied Physics Curtin University of Technology GPO Box U1987 Perth WA 6845 Western Australia Phone: +61 (0)8 9266 4219 Fax: +61 (0)8 9266 2377 Email: ross.willi...@curtin.edu.au -Original Message- From: Jon Wright [mailto:wri...@esrf.fr] Sent: Thursday, 23 July 2009 5:26 AM To: xiu...@ualberta.ca Cc: rietveld_l@ill.fr Subject: Re: LP factor in the Rietveld refinement Sounds like the parameter is the monochromator angle you would need to use to convert an unpolarised beam into a beam with the polarisation state you have (eg, 90 degrees gives 100% polarised). Don't confuse this with the actual monochromator angle at the synchrotron, as the bean is usually polarised before it reaches the monochromator anyway. With some packages you can set the monochromator "roll" angle to put the polarisation in the right plane, depending which way up an area detector was mounted. Good luck, Jon xiu...@ualberta.ca wrote: > Hello, everyone, > > I have some questions about the refinement in Topas. > > When we put the instrument parameters, we always include the LP > factor, and set it to a constant value. I thought LP factor is a > function of theta and not a constant value, so my question is what > exact the constant value means. Why for unpolarized radiation, it is > equal to 0, and for synchrotron radiation it is equal to 90. Sorry to > throw so many questions. > > Thank a lot for any help. > > Xiujun Li > Master Student > Advanced Materials and Processing Laboratory > Chemical and Materials Engineering > University of Alberta > Edmonton, Alberta, Canada T6G 2G6 > Phone: 1-780-492-0701 > No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.392 / Virus Database: 270.13.24/2255 - Release Date: 07/22/09 18:00:00
RE: LP factor in the Rietveld refinement
Hi Xiujun, Jon is correct, but to answer your question fully, the angle is used in an equation to scale the peaks as function of 2theta. If you look in the Technical Reference Manual of TOPAS states that the LP factor (for x-rays) is given by LP = (1 + cos(2th)^2 cos(2th_m)^2) / (cos(theta) sun(theta)^2) 2th_m is the angle mentioned by Jon, ie 26.4° when using Cu Kalpha with a graphic monochromator, 0° when using unpolarised beam, and 90° for full polarised. Or in TOPAS macro language : scale_pks = (1 + Cos(CeV(c,v) Deg)^2 Cos(2 Th)^2) /(Sin(Th)^2 Cos(Th)); The Technical Reference has a derivation of the LP equation above and compares it to parameters used in GSAS and Fullprof. Kind Regards, Ross + Ross Williams PhD Student Centre for Materials Research Department of Imaging and Applied Physics Curtin University of Technology GPO Box U1987 Perth WA 6845 Western Australia Phone: +61 (0)8 9266 4219 Fax: +61 (0)8 9266 2377 Email: ross.willi...@curtin.edu.au -Original Message- From: Jon Wright [mailto:wri...@esrf.fr] Sent: Thursday, 23 July 2009 5:26 AM To: xiu...@ualberta.ca Cc: rietveld_l@ill.fr Subject: Re: LP factor in the Rietveld refinement Sounds like the parameter is the monochromator angle you would need to use to convert an unpolarised beam into a beam with the polarisation state you have (eg, 90 degrees gives 100% polarised). Don't confuse this with the actual monochromator angle at the synchrotron, as the bean is usually polarised before it reaches the monochromator anyway. With some packages you can set the monochromator "roll" angle to put the polarisation in the right plane, depending which way up an area detector was mounted. Good luck, Jon xiu...@ualberta.ca wrote: > Hello, everyone, > > I have some questions about the refinement in Topas. > > When we put the instrument parameters, we always include the LP > factor, and set it to a constant value. I thought LP factor is a > function of theta and not a constant value, so my question is what > exact the constant value means. Why for unpolarized radiation, it is > equal to 0, and for synchrotron radiation it is equal to 90. Sorry to > throw so many questions. > > Thank a lot for any help. > > Xiujun Li > Master Student > Advanced Materials and Processing Laboratory > Chemical and Materials Engineering > University of Alberta > Edmonton, Alberta, Canada T6G 2G6 > Phone: 1-780-492-0701 >
Re: LP factor in the Rietveld refinement
Sounds like the parameter is the monochromator angle you would need to use to convert an unpolarised beam into a beam with the polarisation state you have (eg, 90 degrees gives 100% polarised). Don't confuse this with the actual monochromator angle at the synchrotron, as the bean is usually polarised before it reaches the monochromator anyway. With some packages you can set the monochromator "roll" angle to put the polarisation in the right plane, depending which way up an area detector was mounted. Good luck, Jon xiu...@ualberta.ca wrote: Hello, everyone, I have some questions about the refinement in Topas. When we put the instrument parameters, we always include the LP factor, and set it to a constant value. I thought LP factor is a function of theta and not a constant value, so my question is what exact the constant value means. Why for unpolarized radiation, it is equal to 0, and for synchrotron radiation it is equal to 90. Sorry to throw so many questions. Thank a lot for any help. Xiujun Li Master Student Advanced Materials and Processing Laboratory Chemical and Materials Engineering University of Alberta Edmonton, Alberta, Canada T6G 2G6 Phone: 1-780-492-0701
LP factor in the Rietveld refinement
Hello, everyone, I have some questions about the refinement in Topas. When we put the instrument parameters, we always include the LP factor, and set it to a constant value. I thought LP factor is a function of theta and not a constant value, so my question is what exact the constant value means. Why for unpolarized radiation, it is equal to 0, and for synchrotron radiation it is equal to 90. Sorry to throw so many questions. Thank a lot for any help. Xiujun Li Master Student Advanced Materials and Processing Laboratory Chemical and Materials Engineering University of Alberta Edmonton, Alberta, Canada T6G 2G6 Phone: 1-780-492-0701
Re: I am a newcome, how can I begin my rietveld refinement analysis
Hi, Li: To me, the most wonderful tool to determine initial peakshape parameters is CMPR. CMPR is especially oriented to GSAS and gives you GU, GV, GW etc. And when you use EXPGUI for GSAS, you can also try Graphs->widplt to see how FWHM develops when parameters are tuned. When you prefer Fullprof, you should take a factor to get U, V, W etc. i am not sure about the facor exactly, maybe GX~100X(X=U, V, W), er..? Anyway, just go ahead and make a try. Faithfully Jun Lu -- Lst. Prof. Lijie Qiao Department of Materials Physics and Chemistry University of Science and Technology Beijing 100083 Beijing P.R. China http://www.instrument.com.cn/ilog/handsomeland/ Lst. Prof. Loidl and Lunkenheimer Experimental Physics V Center for Electronic Correlations and Magnetism (EKM) University of Augsburg Universitaetsstr. 2 86159 Augsburg Germany http://www.physik.uni-augsburg.de/exp5 - Original Message - From: "Mingtao Li" <[EMAIL PROTECTED]> To: Sent: Sunday, November 30, 2008 1:11 AM Subject: I am a newcome, how can I begin my rietveld refinement analysis Hi, everyone, I am a newcome to Rietveld refinement. Actually I am a student majored in photocatalytic splitting water for hydrogen production. We want to analysis the structures of our photocatalysts via rietveld method. For that purpose we got a X'pert Pro diffractionmeter from Panalytica about 3 years ago. But rietveld is too difficult to start. Now I have read some books and downloaded some programs from ccp14 such as fullprof, checkcell and so on. Also I have tested some examples. However I am still confused. How can I determine the initial value of some parameters such as U, V and W. Maybe I need a Instrumental Resolution Function file, but how can set that file? Can anybody give me some advice about this? thanks a million. -- Mingtao Li State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'an Jiaotong University Xi'an, 710049 P.R.China Tel: +86-29-8266 8296 Fax: +86-29-8266 9033 Email: [EMAIL PROTECTED]
RIET: Re: I am a newcome, how can I begin my rietveld refinement analysis
Moderate self citation alert follows - the practical notes from the Canadian Powder Diffraction Workshop give starting practical on fitting using GSAS which might help guide starting refinements if you following the manual examples. http://www.cins.ca/cpdw/notes.html Lachlan. At 08:11 AM 11/30/2008 +0800, Mingtao Li wrote: >Hi, everyone, > I am a newcome to Rietveld refinement. Actually I am a student >majored in photocatalytic splitting water for hydrogen production. We >want to analysis the structures of our photocatalysts via rietveld >method. For that purpose we got a X'pert Pro diffractionmeter from >Panalytica about 3 years ago. But rietveld is too difficult to start. >Now I have read some books and downloaded some programs from ccp14 >such as fullprof, checkcell and so on. Also I have tested some >examples. However I am still confused. How can I determine the initial >value of some parameters such as U, V and W. Maybe I need a >Instrumental Resolution Function file, but how can set that file? > >Can anybody give me some advice about this? > >thanks a million. > >-- >Mingtao Li >State Key Laboratory of Multiphase Flow in Power Engineering >School of Energy and Power Engineering >Xi'an Jiaotong University >Xi'an, 710049 >P.R.China >Tel: +86-29-8266 8296 >Fax: +86-29-8266 9033 >Email: [EMAIL PROTECTED] > > --- Lachlan M. D. Cranswick Contact outside working hours / Coordonnees en dehors des heures de travail: NEW E-mail / courriel: lachlanc *at* magma.ca Home Tel: (613) 584-4226 ; Cell/mobile: (613) 401-6254 WWW: http://lachlan.bluehaze.com.au/ P.O. Box 2057, Deep River, Ontario, Canada, K0J 1P0 (please use clear titles in any Email - otherwise messages might accidentally get put in the SPAM list due to large amount of junk Email being received. If you don't get an expected reply to any messages, please try again.) (Essayez d'utiliser des titres explicites - sans quoi vos messages pourraient aboutir dans un dossier de rebuts, du fait de la quantite tres importante de pourriels recue. Si vous n'obtenez pas la reponse attendue, merci de bien vouloir renvoyer un message.)
Re: I am a newcome, how can I begin my rietveld refinement analysis
At the initial stage you don’t need precise values of U, V, and W. You may set U=0, V=0, and W equal to the squared FWHM of the highest peak. Leonid * Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660049, K. Marx 42, Krasnoyarsk, Russia www.icct.ru/eng/content/persons/Sol_LA www.geocities.com/l_solovyov * --- On Sun, 11/30/08, Mingtao Li <[EMAIL PROTECTED]> wrote: Hi, everyone, I am a newcome to Rietveld refinement. Actually I am a student majored in photocatalytic splitting water for hydrogen production. We want to analysis the structures of our photocatalysts via rietveld method. For that purpose we got a X'pert Pro diffractionmeter from Panalytica about 3 years ago. But rietveld is too difficult to start. Now I have read some books and downloaded some programs from ccp14 such as fullprof, checkcell and so on. Also I have tested some examples. However I am still confused. How can I determine the initial value of some parameters such as U, V and W. Maybe I need a Instrumental Resolution Function file, but how can set that file? Can anybody give me some advice about this? thanks a million. -- Mingtao Li State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'an Jiaotong University Xi'an, 710049 P.R.China Tel: +86-29-8266 8296 Fax: +86-29-8266 9033 Email: [EMAIL PROTECTED]
I am a newcome, how can I begin my rietveld refinement analysis
Hi, everyone, I am a newcome to Rietveld refinement. Actually I am a student majored in photocatalytic splitting water for hydrogen production. We want to analysis the structures of our photocatalysts via rietveld method. For that purpose we got a X'pert Pro diffractionmeter from Panalytica about 3 years ago. But rietveld is too difficult to start. Now I have read some books and downloaded some programs from ccp14 such as fullprof, checkcell and so on. Also I have tested some examples. However I am still confused. How can I determine the initial value of some parameters such as U, V and W. Maybe I need a Instrumental Resolution Function file, but how can set that file? Can anybody give me some advice about this? thanks a million. -- Mingtao Li State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'an Jiaotong University Xi'an, 710049 P.R.China Tel: +86-29-8266 8296 Fax: +86-29-8266 9033 Email: [EMAIL PROTECTED]
I am a newcome, how can I begin my rietveld refinement analysis
Hi, everyone, I am a newcome to Rietveld refinement. Actually I am a student majored in photocatalytic splitting water for hydrogen production. We want to analysis the structures of our photocatalysts via rietveld method. For that purpose we got a X'pert Pro diffractionmeter from Panalytica about 3 years ago. But rietveld is too difficult to start. Now I have read some books and downloaded some programs from ccp14 such as fullprof, checkcell and so on. Also I have tested some examples. However I am still confused. How can I determine the initial value of some parameters such as U, V and W. Maybe I need a Instrumental Resolution Function file, but how can set that file? Can anybody give me some advice about this? thanks a million. -- Mingtao Li State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'an Jiaotong University Xi'an, 710049 P.R.China Tel: +86-29-8266 8296 Fax: +86-29-8266 9033 Email: [EMAIL PROTECTED]
Re: 1/Yo**2 weighting scheme in Rietveld refinement
On Mar 14, 2008, at 5:41 AM, Franz Werner wrote:
w=1/Yo**2 [weighting] is proposed ("By using the new weighting
scheme, the accuracy of positional parameters of the test sample
was significantly improved relative to the weight function 1/Yo,
which weights the medium and strong intensities more heavily, is in
accordance with statistical theory and gives a better overall fit
between the observed and calculated powder patterns.").
I'll give my stock comment in response. For fitting of data with only
statistical errors, you obtain the smallest uncertainties on the fit
parameters when weighting is w = sigma**-2. This requires that you
know the experimental uncertainties (no image plates or other non-
quanta counting detectors). Further, if your data have only
statistical errors, then chi**2 ~= 1. Any other weighting scheme is
effectively throwing away data.
In cases where there are non-statistical error sources, then you do
gain by down-weighting the data most effected by systematic errors.
However, be aware that the systematic error you are choosing to
reject could be trying to tell you that really would want to know:
e.g. the model you are using is incomplete or even wrong.
If you have reason to believe that your measurements are inaccurate
in a particular way (for example uncorrected deadtime, sample
roughness, or funky peak shapes, etc) it might make sense to change
the weighting function, but I personally don't think there is a
generic source of error in all diffraction measurements that would
make it appropriate to use the same weighting change for all types of
data and materials.
Brian
1/Yo**2 weighting scheme in Rietveld refinement
Dear Rietvelders
I just stumbled on the paper "Weighting Scheme for the Minimization Function in
Rietveld Refinement" (H. Toraya, http://dx.doi.org/10.1107/S0021889897011096)
where w=1/Yo**2 is proposed ("By using the new weighting scheme, the accuracy
of positional parameters of the test sample was significantly improved relative
to the weight function 1/Yo, which weights the medium and strong intensities
more heavily, is in accordance with statistical theory and gives a better
overall fit between the observed and calculated powder patterns.").
Does anyone have experience with this weighting scheme?
Thanks for your advise.
Franz Werner
--
Psst! Geheimtipp: Online Games kostenlos spielen bei den GMX Free Games!
http://games.entertainment.gmx.net/de/entertainment/games/free
Powder Diffraction and Rietveld Refinement School, Durham
Dear All, On behalf of the Physical Crystallography Group of the British Crystallographic Association, I am pleased to announce the Powder Diffraction and Rietveld Refinement School at Durham University, 30th March-3rd April 2008. Lectures will be given by Jeremy Cockcroft, Andy Fitch, John Evans and Ivana Evans. There will also be small group tutorials and a large number of practical hands-on computer sessions. Topics to be covered will include: · Data collection strategies for X-ray and neutron diffraction · Constant wavelength and time of flight diffraction · Modelling peak shapes · Indexing powder patterns · Rietveld, Le Bail and Pawley fitting methods · X-ray and neutron combined Rietveld refinement · Extended solids and molecular systems · Restrained refinements · Rigid body refinements Accommodation will be at a Durham College and lectures/computer workshops will be held in the Chemistry Department. We have managed to raise significant sponsorship from EPSRC, PCG and IUCr, and will be able to offer a significant number of bursaries to the UK students and a smaller number of bursaries to overseas participants. The number of participants is limited and applications are accepted online, via the school website: http://www.dur.ac.uk/john.evans/webpages/pcg_rietveld_school_2008.htm. For more information please email [EMAIL PROTECTED] or [EMAIL PROTECTED] Dr. Ivana Radosavljevic Evans Academic Fellow in Structural/Materials Chemistry Department of Chemistry University of Durham Science Site Durham DH1 3LE, U.K. Office: CG 244 Phone: (0191) 334-2594 Fax: (0191) 384-4737 www.dur.ac.uk/ivana.radosavljevic
Parameters in Rietveld refinement
Forwarded from Mike Glazer: I think that very often people tend to overlook what is in fact the primary purpose of Rietveld: it is to get structural parameters out that have some meaning. The Rietveld method consists of two sets of refinement variables. First of all you have the structural parameters (atomic positions, displacement parameters, site occupation etc) and secondly instrumental type parameters whose purpose is to enable fitting of the profiles. In my experience playing around with different line shapes and profile parameters (within reason) usually has a relatively minor effect on the structural parameters, especially atomic positions. What they do however is to make the profile fit look nicer and give you lower R factors. And then everyone feels happier. However, the importance of Rietveld is in the structural parameters that you get out. The meanings of the instrumental parameters are fairly obtuse as this is where most of the errors end up. The U V W parameters of Cagliotti are meaningless. To see this, the next time you do a refinement with U V and W take a look at the correlation matrix between these parameters: you will see that they are invariably almost 100% correlated. That is why in fact you are probably better to fix one and refine just two. It for this reason also that I have little faith in the meaning of refined parameters such as preferred orientation, except perhaps in some very rough sense. Mike Glazer _ Dr Alan Hewat, ILL Grenoble, FRANCE <[EMAIL PROTECTED]>fax+33.476.20.76.48 +33.476.20.72.13 (.26 Mme Guillermet) http://www.ill.fr/dif/people/hewat/ _ Alan I wanted to send the following to the Rietveld group but it was rejected. Any ideas? I think that very often people tend to overlook what is in fact the primary purpose of Rietveld: it is to get structural parameters out that have some meaning. The Rietveld method consists of two sets of refinement variables. First of all you have the structural parameters (atomic positions, displacement parameters, site occupation etc) and secondly instrumental type parameters whose purpose is to enable fitting of the profiles. In my experience playing around with different line shapes and profile parameters (within reason) usually has a relatively minor effect on the structural parameters, especially atomic positions. What they do however is to make the profile fit look nicer and give you lower R factors. And then everyone feels happier. However, the importance of Rietveld is in the structural parameters that you get out. The meanings of the instrumental parameters are fairly obtuse as this is where most of the errors end up. The U V W parameters of Cagliotti are meaningless. To see this, the next time you do a refinement with U V and W take a look at the correlation matrix between these parameters: you will see that they are invariably almost 100% correlated. That is why in fact you are probably better to fix one and refine just two. It for this reason also that I have little faith in the meaning of refined parameters such as preferred orientation, except perhaps in some very rough sense. Mike Glazer<>
RE: Re: Problems using TOPAS R (Rietveld refinement)
Makes sense with ultra-fines. My portlandite grains were 5 microns upwards. I'm working to avoid ultra-fines even harder than the bigger stuff :-) Pam From: Omotoso, Oladipo [mailto:[EMAIL PROTECTED] Sent: Wed 21/03/2007 10:47 AM To: rietveld_l@ill.fr Subject: Re: Problems using TOPAS R (Rietveld refinement) My limited experience with X-ray capillary measurements of ultra fine clay minerals suggests that you could have significant preferred orientation along the b* axis. It is actually a good way of determining aspect ratios in phyllosilicates. Dipo Omotoso From: Whitfield, Pamela [mailto:[EMAIL PROTECTED] Sent: Wednesday, March 21, 2007 7:51 AM To: rietveld_l@ill.fr Subject: RE: Re: Problems using TOPAS R (Rietveld refinement) I have to disagree with that; at least on a practical front with lab XRD. I have done measurements myself with samples containing large portlandite plates (granted, not a silicate but lovely-looking plates in a SEM) for quantitative analysis. The whole point of the work was to see if capillary measurements would be worth it if the normal sample prep techniques would change the nature of the sample. The reflection measurements had awful orientation, but the portlandite spherical harmonics PO coefficients for the capillary data gave a texture index of 1, i.e. an ideal powder. The diffraction optics and detector were identical for reflection and transmission. The capillary data actually gave better quantitative results than the reflection. A reason might be that if the grains are large enough to orientate significantly they might be big enough to cause microabsorption effects that are best avoided (the Brindley correction assumes spherical particles so plates are a bit of a headache). It's just a thought, but the orientation in neutron and X-ray data might differ due to the difference in sample container size and orientation. Neutron cans are often mounted vertically and are pretty big so there won't be much advantage over reflection as the material settles. Lab capillaries are usually mounted horizontally and the capillary diameter is often quite small in relation to the grain size (compared to neutron sample cans). All bets are off for wollastonite though! I will shut up at this point as I trying to avoid doing clay analysis! Pam -Original Message- From: David L. Bish [mailto:[EMAIL PROTECTED] Sent: March 21, 2007 9:11 AM To: rietveld_l@ill.fr Subject: Re: Problems using TOPAS R (Rietveld refinement) One often hears of attempts to "eliminate" preferred orientation in diffraction patterns of layer silicates using transmission measurements. Keep in mind that if PO is a problem in reflection geometry, it will also affect transmission measurements, in a manner potentially similar to flat-plate samples. We did some TOF neutron measurements on phyllosilicates a few years ago with what amounts to capillary sample holders, and preferred orientation was a significant problem. If a material orients, it will do so in all mounts unless steps are taken to minimize it. Dave At 07:50 AM 3/21/2007 +0100, you wrote: Gentlemen, I've been listening for a week or so and I am really wondering what do you want to get ... Actually you are setting up a "refinement", whose results will be, at least, inaccurate. I am always surprised by attempts to refine crystal structure of a disordered sheet silicate from powders, especially when it is known it hardly works with single crystal data. Yes, there are several models of disorder, but who has ever proved they are really good ? I do not mean here a graphical comparison of powder patterns with a calculated trace, but a comparison of structure factors or integrated intensities. (Which ones are to be selected is well described in the works of my colleague, S.Durovic and his co-workers.) As far as powders are concerned, all sheet silicates "suffer" from prefered orientation along 001. Until you have a pattern taken in a capillary or in transmission mode, this effect will be dominating and you can forget such noble problems like anisotropic broadening. Last but not least : quantitative phase analysis by "Rietveld" is (when only scale factors are "on") nothing else but multiple linear regression. There is a huge volume of literature on the topic, especially which variables must, which should and which could be a part of your model. I really wonder why the authors of program do not add one option called "QUAN", which could, upon convergence of highly sophisticat
Re: Problems using TOPAS R (Rietveld refinement)
My limited experience with X-ray capillary measurements of ultra fine clay minerals suggests that you could have significant preferred orientation along the b* axis. It is actually a good way of determining aspect ratios in phyllosilicates. Dipo Omotoso From: Whitfield, Pamela [mailto:[EMAIL PROTECTED] Sent: Wednesday, March 21, 2007 7:51 AM To: rietveld_l@ill.fr Subject: RE: Re: Problems using TOPAS R (Rietveld refinement) I have to disagree with that; at least on a practical front with lab XRD. I have done measurements myself with samples containing large portlandite plates (granted, not a silicate but lovely-looking plates in a SEM) for quantitative analysis. The whole point of the work was to see if capillary measurements would be worth it if the normal sample prep techniques would change the nature of the sample. The reflection measurements had awful orientation, but the portlandite spherical harmonics PO coefficients for the capillary data gave a texture index of 1, i.e. an ideal powder. The diffraction optics and detector were identical for reflection and transmission. The capillary data actually gave better quantitative results than the reflection. A reason might be that if the grains are large enough to orientate significantly they might be big enough to cause microabsorption effects that are best avoided (the Brindley correction assumes spherical particles so plates are a bit of a headache). It's just a thought, but the orientation in neutron and X-ray data might differ due to the difference in sample container size and orientation. Neutron cans are often mounted vertically and are pretty big so there won't be much advantage over reflection as the material settles. Lab capillaries are usually mounted horizontally and the capillary diameter is often quite small in relation to the grain size (compared to neutron sample cans). All bets are off for wollastonite though! I will shut up at this point as I trying to avoid doing clay analysis! Pam -Original Message- From: David L. Bish [mailto:[EMAIL PROTECTED] Sent: March 21, 2007 9:11 AM To: rietveld_l@ill.fr Subject: Re: Problems using TOPAS R (Rietveld refinement) One often hears of attempts to "eliminate" preferred orientation in diffraction patterns of layer silicates using transmission measurements. Keep in mind that if PO is a problem in reflection geometry, it will also affect transmission measurements, in a manner potentially similar to flat-plate samples. We did some TOF neutron measurements on phyllosilicates a few years ago with what amounts to capillary sample holders, and preferred orientation was a significant problem. If a material orients, it will do so in all mounts unless steps are taken to minimize it. Dave At 07:50 AM 3/21/2007 +0100, you wrote: Gentlemen, I've been listening for a week or so and I am really wondering what do you want to get ... Actually you are setting up a "refinement", whose results will be, at least, inaccurate. I am always surprised by attempts to refine crystal structure of a disordered sheet silicate from powders, especially when it is known it hardly works with single crystal data. Yes, there are several models of disorder, but who has ever proved they are really good ? I do not mean here a graphical comparison of powder patterns with a calculated trace, but a comparison of structure factors or integrated intensities. (Which ones are to be selected is well described in the works of my colleague, S.Durovic and his co-workers.) As far as powders are concerned, all sheet silicates "suffer" from prefered orientation along 001. Until you have a pattern taken in a capillary or in transmission mode, this effect will be dominating and you can forget such noble problems like anisotropic broadening. Last but not least : quantitative phase analysis by "Rietveld" is (when only scale factors are "on") nothing else but multiple linear regression. There is a huge volume of literature on the topic, especially which variables must, which should and which could be a part of your model. I really wonder why the authors of program do not add one option called "QUAN", which could, upon convergence of highly sophisticated non-linear L-S, fix all parameters but scale factors and run standard tests or factor analysis. One more diagonalization is not very time consuming, is it ? To avoid numerical problems, I'd use SVD. This idea is free and if it helps people reporting 0.1% MgO (SiO2) in a mixture of 10 phases t
RE: Problems using TOPAS R (Rietveld refinement)
Lubo SVD as you mentioned does avoid numerical problems as does other methods such as the conjugate gradient method. SVD minimizes on the residuals |A x - b| after solving the matrix equation A x = b. I would like to point out however that errors obtained from the covariance matrix are an approximation. The idea of fixing parameters as in SVD when a singular value is encountered is also a little arbitrary as it requires the user setting a lower limit. The A matrix is formed at a point in parameter space; when there are strong correlations (as SVD would report) then that point in space changes from one refinement to another after modifying the parameter slightly. If derivatives are numerically calculated, as is the case for convolution parameters, then the A matrix becomes a function of how the derivative are calculated; forward difference approximation for example gives different derivatives than both forward and backwards if the step size in the derivative is appreciable. For most convolutions and numerical derivatives in general then it needs to be appreciable for good convergence. Rietveld people may want to look at the re-sampling technique known as the bootstrap method of error determination. It gives similar errors to the covariance matrix when the correlations are weak; the maths journals are full of details. It requires some more computing time but it actually gives the distribution. And yes TOPAS has the bootstrap method; other code writers may wish to investigate it. Cheers Alan -Original Message- From: Lubomir Smrcok [mailto:[EMAIL PROTECTED] Sent: Wednesday, 21 March 2007 5:50 PM To: rietveld_l@ill.fr Subject: Re: Problems using TOPAS R (Rietveld refinement) Gentlemen, I've been listening for a week or so and I am really wondering what do you want to get ... Actually you are setting up a "refinement", whose results will be, at least, inaccurate. I am always surprised by attempts to refine crystal structure of a disordered sheet silicate from powders, especially when it is known it hardly works with single crystal data. Yes, there are several models of disorder, but who has ever proved they are really good ? I do not mean here a graphical comparison of powder patterns with a calculated trace, but a comparison of structure factors or integrated intensities. (Which ones are to be selected is well described in the works of my colleague, S.Durovic and his co-workers.) As far as powders are concerned, all sheet silicates "suffer" from prefered orientation along 001. Until you have a pattern taken in a capillary or in transmission mode, this effect will be dominating and you can forget such noble problems like anisotropic broadening. Last but not least : quantitative phase analysis by "Rietveld" is (when only scale factors are "on") nothing else but multiple linear regression. There is a huge volume of literature on the topic, especially which variables must, which should and which could be a part of your model. I really wonder why the authors of program do not add one option called "QUAN", which could, upon convergence of highly sophisticated non-linear L-S, fix all parameters but scale factors and run standard tests or factor analysis. One more diagonalization is not very time consuming, is it ? To avoid numerical problems, I'd use SVD. This idea is free and if it helps people reporting 0.1% MgO (SiO2) in a mixture of 10 phases to think a little of the numbers they are getting, I would only be happy :-) Lubo P.S. Hereby I declare I have never used Topas and I am thus not familiar with all its advantages or disadvantages compared to other codes. On Wed, 21 Mar 2007, Reinhard Kleeberg wrote: > Dear Leandro Bravo, > some comments below: > > Leandro Bravo schrieb: > > > > > In the refinement of chlorite minerals with well defined disordering > > (layers shifting by exactly b/3 along the three pseudohexagonal Y > > axis), you separate the peaks into k = 3.n (relative sharp, less > > intensive peak) and k 3.n (broadened or disappeared > > reflections). How did you determined this value k = 3.n and n = > > 0,1,2,3..., right? > > > The occurence of stacking faults along the pseudohexagonal Y axes causes > broadening of all reflections hkl with k unequal 3n (for example 110, > 020, 111..) whereas the reflections with k equal 3n remain unaffected > (001, 131, 060, 331...). This is clear from geometric conditions, and > can be seen in single crystal XRD (oscillation photographs, Weissenberg > photographs) as well in selected area electron diffraction patterns. The > fact is known for a long time, and published and discussed in standard > textbooks, for example *Brindley, G.W., Brown, G.: Crystal Structures > of Clay Minerals and their X-ray Identification. Mineralogical Society, > London, 1980.* > > > First, the chlori
RE: Re: Problems using TOPAS R (Rietveld refinement)
I have to disagree with that; at least on a practical front with lab XRD. I have done measurements myself with samples containing large portlandite plates (granted, not a silicate but lovely-looking plates in a SEM) for quantitative analysis. The whole point of the work was to see if capillary measurements would be worth it if the normal sample prep techniques would change the nature of the sample. The reflection measurements had awful orientation, but the portlandite spherical harmonics PO coefficients for the capillary data gave a texture index of 1, i.e. an ideal powder. The diffraction optics and detector were identical for reflection and transmission. The capillary data actually gave better quantitative results than the reflection. A reason might be that if the grains are large enough to orientate significantly they might be big enough to cause microabsorption effects that are best avoided (the Brindley correction assumes spherical particles so plates are a bit of a headache). It's just a thought, but the orientation in neutron and X-ray data might differ due to the difference in sample container size and orientation. Neutron cans are often mounted vertically and are pretty big so there won't be much advantage over reflection as the material settles. Lab capillaries are usually mounted horizontally and the capillary diameter is often quite small in relation to the grain size (compared to neutron sample cans). All bets are off for wollastonite though! I will shut up at this point as I trying to avoid doing clay analysis! Pam -Original Message- From: David L. Bish [mailto:[EMAIL PROTECTED] Sent: March 21, 2007 9:11 AM To: rietveld_l@ill.fr Subject: Re: Problems using TOPAS R (Rietveld refinement) One often hears of attempts to "eliminate" preferred orientation in diffraction patterns of layer silicates using transmission measurements. Keep in mind that if PO is a problem in reflection geometry, it will also affect transmission measurements, in a manner potentially similar to flat-plate samples. We did some TOF neutron measurements on phyllosilicates a few years ago with what amounts to capillary sample holders, and preferred orientation was a significant problem. If a material orients, it will do so in all mounts unless steps are taken to minimize it. Dave At 07:50 AM 3/21/2007 +0100, you wrote: Gentlemen, I've been listening for a week or so and I am really wondering what do you want to get ... Actually you are setting up a "refinement", whose results will be, at least, inaccurate. I am always surprised by attempts to refine crystal structure of a disordered sheet silicate from powders, especially when it is known it hardly works with single crystal data. Yes, there are several models of disorder, but who has ever proved they are really good ? I do not mean here a graphical comparison of powder patterns with a calculated trace, but a comparison of structure factors or integrated intensities. (Which ones are to be selected is well described in the works of my colleague, S.Durovic and his co-workers.) As far as powders are concerned, all sheet silicates "suffer" from prefered orientation along 001. Until you have a pattern taken in a capillary or in transmission mode, this effect will be dominating and you can forget such noble problems like anisotropic broadening. Last but not least : quantitative phase analysis by "Rietveld" is (when only scale factors are "on") nothing else but multiple linear regression. There is a huge volume of literature on the topic, especially which variables must, which should and which could be a part of your model. I really wonder why the authors of program do not add one option called "QUAN", which could, upon convergence of highly sophisticated non-linear L-S, fix all parameters but scale factors and run standard tests or factor analysis. One more diagonalization is not very time consuming, is it ? To avoid numerical problems, I'd use SVD. This idea is free and if it helps people reporting 0.1% MgO (SiO2) in a mixture of 10 phases to think a little of the numbers they are getting, I would only be happy :-) Lubo P.S. Hereby I declare I have never used Topas and I am thus not familiar
Re: Problems using TOPAS R (Rietveld refinement)
One often hears of attempts to "eliminate" preferred orientation in diffraction patterns of layer silicates using transmission measurements. Keep in mind that if PO is a problem in reflection geometry, it will also affect transmission measurements, in a manner potentially similar to flat-plate samples. We did some TOF neutron measurements on phyllosilicates a few years ago with what amounts to capillary sample holders, and preferred orientation was a significant problem. If a material orients, it will do so in all mounts unless steps are taken to minimize it. Dave At 07:50 AM 3/21/2007 +0100, you wrote: Gentlemen, I've been listening for a week or so and I am really wondering what do you want to get ... Actually you are setting up a "refinement", whose results will be, at least, inaccurate. I am always surprised by attempts to refine crystal structure of a disordered sheet silicate from powders, especially when it is known it hardly works with single crystal data. Yes, there are several models of disorder, but who has ever proved they are really good ? I do not mean here a graphical comparison of powder patterns with a calculated trace, but a comparison of structure factors or integrated intensities. (Which ones are to be selected is well described in the works of my colleague, S.Durovic and his co-workers.) As far as powders are concerned, all sheet silicates "suffer" from prefered orientation along 001. Until you have a pattern taken in a capillary or in transmission mode, this effect will be dominating and you can forget such noble problems like anisotropic broadening. Last but not least : quantitative phase analysis by "Rietveld" is (when only scale factors are "on") nothing else but multiple linear regression. There is a huge volume of literature on the topic, especially which variables must, which should and which could be a part of your model. I really wonder why the authors of program do not add one option called "QUAN", which could, upon convergence of highly sophisticated non-linear L-S, fix all parameters but scale factors and run standard tests or factor analysis. One more diagonalization is not very time consuming, is it ? To avoid numerical problems, I'd use SVD. This idea is free and if it helps people reporting 0.1% MgO (SiO2) in a mixture of 10 phases to think a little of the numbers they are getting, I would only be happy :-) Lubo P.S. Hereby I declare I have never used Topas and I am thus not familiar with all its advantages or disadvantages compared to other codes. On Wed, 21 Mar 2007, Reinhard Kleeberg wrote: > Dear Leandro Bravo, > some comments below: > > Leandro Bravo schrieb: > > > > > In the refinement of chlorite minerals with well defined disordering > > (layers shifting by exactly b/3 along the three pseudohexagonal Y > > axis), you separate the peaks into k = 3.n (relative sharp, less > > intensive peak) and k 3.n (broadened or disappeared > > reflections). How did you determined this value k = 3.n and n = > > 0,1,2,3..., right? > > > The occurence of stacking faults along the pseudohexagonal Y axes causes > broadening of all reflections hkl with k unequal 3n (for example 110, > 020, 111..) whereas the reflections with k equal 3n remain unaffected > (001, 131, 060, 331...). This is clear from geometric conditions, and > can be seen in single crystal XRD (oscillation photographs, Weissenberg > photographs) as well in selected area electron diffraction patterns. The > fact is known for a long time, and published and discussed in standard > textbooks, for example *Brindley, G.W., Brown, G.: Crystal Structures > of Clay Minerals and their X-ray Identification. Mineralogical Society, > London, 1980.* > > > First, the chlorite refinement. > > > > In the first refinement of chlorite you used no disordering models and > > used ´´cell parameters`` and ´´occupation of octahedra``. So you > > refined the lattice parameters and the occupancy of all atoms? > > Yes, the lattice parameters. > Only the occupation/substitution of atoms with significant difference in > scattering power can be refined in powder diffraction. In case of > chlorites, the substitution Fe-Mg at the 4 octahedral positions can be > refined. > > > > > In the second refinement, you use na anisotropic line broadening ´´in > > the traditional way``. So you used a simple ellipsoidal model and/or > > spherical harmonics? > > > Simple ellipsoidal model, assuming very thiny platy crystals. But it was > clear that this model must fail, see above the known fact of disorder in > layer stacking. And from microscopy it is clear that the "crystals" are > much too large to produce significant line broadening from size effects. > You can see this for a lot of clay minerals: If the "ellipsoidal > crystallite shape" model would be ok, the 00l reflections would have the > broadest lines, and the 110, 020 and so on should be the sharpest ones. > But this is not true in practice, mostly the hkl are terribly broadene
RE: Problems using TOPAS R (Rietveld refinement)
Clay people I think the single crystal analysis of clays is interesting. I have not read the literature but in determining the intensities is overlap of the dots considered as I would have expected the dots to be very much smeared (5 to 10 degrees 2Th in my experience). If yes the fitting in two dimension would be better. Thus the question to ask is how accurate can QPA be for clays if the intensities can be accurately obtained; is this an open question or is the book closed on this. If as Reinhard Kleeberg mentioned that some directions are unaffected then it would seem plausible that something can be gained especially if one of "those models" work. Also, TOPAS simply offers a means of describing the peak shapes using a hkl dependent spherical harmonics. From my experiences it seems to work. Like Lubomir Smrcok remarked getting the intensities is critical. Another important point, again as Lubomir Smrcok mentioned, is preferred orientation. If there's very strong preferred orientation then the peak shapes will be affected due to axial divergence as well; it best to remove preferred orientation. Cheers Alan -Original Message- From: Reinhard Kleeberg [mailto:[EMAIL PROTECTED] Sent: Wednesday, 21 March 2007 7:48 PM To: rietveld_l@ill.fr Subject: Re: Problems using TOPAS R (Rietveld refinement) Dear colleagues, sorry, my mail should go directly to Leandro, but I used this damned reply buttom... My answer was related to Leandro's questions regarding these line broadening models. I realised that Leandro is going on to apply a Rietveld program for phase quantification, including kaolinite and later other clay minerals. I only tried to express my personal experience, that any inadequate profile description of a clay mineral will surely cause wrong QPA results, nothing else. This is a practical issue, and it is only partially related to structure refinement. Lubomir Smrcok is definitely right that other things like PO are frequently biasing a QPA result, but for the most of these problems working solutions do exist. But I disagree that anisotropic line broadening is a "noble problem". In clay mineral mixtures, it is essentially to fit the profiles of the single phases as best as one can, to get any reasonable "QPA" result in a +-5 wt% interval. On the other hand, for the QPA purpose it is not so much important to find any sophisticated description of the microstructure of a phase. But the "model" should be flexible enough to cover the variablility of the profiles in a given system, and, on the other hand, stabil enough (not over-parametrised) to work in mixtures. The balancing out of these two issues could be the matter of an endless debate. And here I agree again, a better, more stable minimisation algorithm can help to keep a maximum of flexibility of the models. Best regards Reinhard Kleeberg Lubomir Smrcok schrieb: >Gentlemen, >I've been listening for a week or so and I am really wondering what do >you want to get ... Actually you are setting up a "refinement", whose >results will be, at least, inaccurate. I am always surprised by >attempts to refine crystal structure of a disordered sheet silicate >from powders, especially when it is known it hardly works with single >crystal data. Yes, there are several models of disorder, but who has ever proved they are really good ? >I do not mean here a graphical comparison of powder patterns with a >calculated trace, but a comparison of structure factors or integrated >intensities. (Which ones are to be selected is well described in the >works of my colleague, S.Durovic and his co-workers.) As far as powders >are concerned, all sheet silicates "suffer" from prefered orientation >along 001. Until you have a pattern taken in a capillary or in >transmission mode, this effect will be dominating and you can forget >such noble problems like anisotropic broadening. > >Last but not least : quantitative phase analysis by "Rietveld" is (when >only scale factors are "on") nothing else but multiple linear >regression. There is a huge volume of literature on the topic, >especially which variables must, which should and which could be a part of your model. >I really wonder why the authors of program do not add one option called >"QUAN", which could, upon convergence of highly sophisticated >non-linear L-S, fix all parameters but scale factors and run standard >tests or factor analysis. One more diagonalization is not very time >consuming, is it ? To avoid numerical problems, I'd use SVD. >This idea is free and if it helps people reporting 0.1% MgO (SiO2) in a >mixture of 10 phases to think a little of the numbers they are >getting, I would only be happy :-) Lubo > >P.S. Hereby I declare I have never used Topas and I am thus not >fa
Re: Problems using TOPAS R (Rietveld refinement)
Dear colleagues, sorry, my mail should go directly to Leandro, but I used this damned reply buttom... My answer was related to Leandro's questions regarding these line broadening models. I realised that Leandro is going on to apply a Rietveld program for phase quantification, including kaolinite and later other clay minerals. I only tried to express my personal experience, that any inadequate profile description of a clay mineral will surely cause wrong QPA results, nothing else. This is a practical issue, and it is only partially related to structure refinement. Lubomir Smrcok is definitely right that other things like PO are frequently biasing a QPA result, but for the most of these problems working solutions do exist. But I disagree that anisotropic line broadening is a "noble problem". In clay mineral mixtures, it is essentially to fit the profiles of the single phases as best as one can, to get any reasonable "QPA" result in a +-5 wt% interval. On the other hand, for the QPA purpose it is not so much important to find any sophisticated description of the microstructure of a phase. But the "model" should be flexible enough to cover the variablility of the profiles in a given system, and, on the other hand, stabil enough (not over-parametrised) to work in mixtures. The balancing out of these two issues could be the matter of an endless debate. And here I agree again, a better, more stable minimisation algorithm can help to keep a maximum of flexibility of the models. Best regards Reinhard Kleeberg Lubomir Smrcok schrieb: Gentlemen, I've been listening for a week or so and I am really wondering what do you want to get ... Actually you are setting up a "refinement", whose results will be, at least, inaccurate. I am always surprised by attempts to refine crystal structure of a disordered sheet silicate from powders, especially when it is known it hardly works with single crystal data. Yes, there are several models of disorder, but who has ever proved they are really good ? I do not mean here a graphical comparison of powder patterns with a calculated trace, but a comparison of structure factors or integrated intensities. (Which ones are to be selected is well described in the works of my colleague, S.Durovic and his co-workers.) As far as powders are concerned, all sheet silicates "suffer" from prefered orientation along 001. Until you have a pattern taken in a capillary or in transmission mode, this effect will be dominating and you can forget such noble problems like anisotropic broadening. Last but not least : quantitative phase analysis by "Rietveld" is (when only scale factors are "on") nothing else but multiple linear regression. There is a huge volume of literature on the topic, especially which variables must, which should and which could be a part of your model. I really wonder why the authors of program do not add one option called "QUAN", which could, upon convergence of highly sophisticated non-linear L-S, fix all parameters but scale factors and run standard tests or factor analysis. One more diagonalization is not very time consuming, is it ? To avoid numerical problems, I'd use SVD. This idea is free and if it helps people reporting 0.1% MgO (SiO2) in a mixture of 10 phases to think a little of the numbers they are getting, I would only be happy :-) Lubo P.S. Hereby I declare I have never used Topas and I am thus not familiar with all its advantages or disadvantages compared to other codes. On Wed, 21 Mar 2007, Reinhard Kleeberg wrote: Dear Leandro Bravo, some comments below: Leandro Bravo schrieb: In the refinement of chlorite minerals with well defined disordering (layers shifting by exactly b/3 along the three pseudohexagonal Y axis), you separate the peaks into k = 3.n (relative sharp, less intensive peak) and k 3.n (broadened or disappeared reflections). How did you determined this value k = 3.n and n = 0,1,2,3..., right? The occurence of stacking faults along the pseudohexagonal Y axes causes broadening of all reflections hkl with k unequal 3n (for example 110, 020, 111..) whereas the reflections with k equal 3n remain unaffected (001, 131, 060, 331...). This is clear from geometric conditions, and can be seen in single crystal XRD (oscillation photographs, Weissenberg photographs) as well in selected area electron diffraction patterns. The fact is known for a long time, and published and discussed in standard textbooks, for example *Brindley, G.W., Brown, G.: Crystal Structures of Clay Minerals and their X-ray Identification. Mineralogical Society, London, 1980.* First, the chlorite refinement. In the first refinement of chlorite you used no disordering models and used ´´cell parameters`` and ´´occupation of octahedra``. So you refined the lattice parameters and the occupancy of all atoms? Yes, the lattice parameters. Only the occupation/substitution of atoms with significant difference in scattering power can be r
Re: Problems using TOPAS R (Rietveld refinement)
Dear Lubomir Smrock, linear pattern analysis is _not_ Rietveld, this was a common QPA method prior to Rietveld QPA. In a Rietvel QPA, one must refine the lattice parameter at least. And that makes it nonlinear. Depending on the sample, one may decide to add more nonlinear details to the refinement. Of course, additional knowledge about the phases in the sample is welcome. For example: Stacking faults in clay minerals are known to be common from single crystal or electron microscopy investigations. Some phases are known to have sheet- or needle-like shape, e.g. from scanning electron microscopy; therefore anisotropic, hkl-dependant line broadening and/or strong preferred orientation must be concerned. Only seldom such "phases real structure" is derived from the pattern itself. But knowing them Rietveld QPA must introduce and refine them for good results. Regards Joerg Bergmann, Dresden Am Mittwoch, den 21.03.2007, 07:50 +0100 schrieb Lubomir Smrcok: > Gentlemen, > I've been listening for a week or so and I am really wondering what do you > want to get ... Actually you are setting up a "refinement", whose results > will be, at least, inaccurate. I am always surprised by attempts to refine > crystal structure of a disordered sheet silicate from powders, especially > when it is known it hardly works with single crystal data. Yes, there are > several models of disorder, but who has ever proved they are really good ? > I do not mean here a graphical comparison of powder patterns with a > calculated trace, but a comparison of structure factors or integrated > intensities. (Which ones are to be selected is well described in the works > of my colleague, S.Durovic and his co-workers.) > As far as powders are concerned, all sheet silicates "suffer" from > prefered orientation along 001. Until you have a pattern taken in a > capillary or in transmission mode, this effect will be dominating and you > can forget such noble problems like anisotropic broadening. > > Last but not least : quantitative phase analysis by "Rietveld" is (when only > scale factors are "on") nothing else but multiple linear regression. There > is a huge volume of literature on the topic, especially which variables > must, which should and which could be a part of your model. > I really wonder why the authors of program do not add one option called > "QUAN", which could, upon convergence of highly sophisticated non-linear > L-S, fix all parameters but scale factors and run standard tests or factor > analysis. One more diagonalization is not very time consuming, is it ? To > avoid numerical problems, I'd use SVD. > This idea is free and if it helps people reporting 0.1% MgO (SiO2) in a > mixture of 10 phases to think a little of the numbers they are getting, I > would only be happy :-) > Lubo > > P.S. Hereby I declare I have never used Topas and I am thus not familiar > with all its advantages or disadvantages compared to other codes. > > > On Wed, 21 Mar 2007, Reinhard Kleeberg wrote: > > > Dear Leandro Bravo, > > some comments below: > > > > Leandro Bravo schrieb: > > > > > > > > In the refinement of chlorite minerals with well defined disordering > > > (layers shifting by exactly b/3 along the three pseudohexagonal Y > > > axis), you separate the peaks into k = 3.n (relative sharp, less > > > intensive peak) and k 3.n (broadened or disappeared > > > reflections). How did you determined this value k = 3.n and n = > > > 0,1,2,3..., right? > > > > > The occurence of stacking faults along the pseudohexagonal Y axes causes > > broadening of all reflections hkl with k unequal 3n (for example 110, > > 020, 111..) whereas the reflections with k equal 3n remain unaffected > > (001, 131, 060, 331...). This is clear from geometric conditions, and > > can be seen in single crystal XRD (oscillation photographs, Weissenberg > > photographs) as well in selected area electron diffraction patterns. The > > fact is known for a long time, and published and discussed in standard > > textbooks, for example *Brindley, G.W., Brown, G.: Crystal Structures > > of Clay Minerals and their X-ray Identification. Mineralogical Society, > > London, 1980.* > > > > > First, the chlorite refinement. > > > > > > In the first refinement of chlorite you used no disordering models and > > > used ´´cell parameters`` and ´´occupation of octahedra``. So you > > > refined the lattice parameters and the occupancy of all atoms? > > > > Yes, the lattice parameters. > > Only the occupation/substitution of atoms with significant difference in > > scattering power can be refined in powder diffraction. In case of > > chlorites, the substitution Fe-Mg at the 4 octahedral positions can be > > refined. > > > > > > > > In the second refinement, you use na anisotropic line broadening ´´in > > > the traditional way``. So you used a simple ellipsoidal model and/or > > > spherical harmonics? > > > > > Simple ellipsoidal model, assuming very thiny platy crystals. But it was > > clear
Re: Problems using TOPAS R (Rietveld refinement)
Gentlemen, I've been listening for a week or so and I am really wondering what do you want to get ... Actually you are setting up a "refinement", whose results will be, at least, inaccurate. I am always surprised by attempts to refine crystal structure of a disordered sheet silicate from powders, especially when it is known it hardly works with single crystal data. Yes, there are several models of disorder, but who has ever proved they are really good ? I do not mean here a graphical comparison of powder patterns with a calculated trace, but a comparison of structure factors or integrated intensities. (Which ones are to be selected is well described in the works of my colleague, S.Durovic and his co-workers.) As far as powders are concerned, all sheet silicates "suffer" from prefered orientation along 001. Until you have a pattern taken in a capillary or in transmission mode, this effect will be dominating and you can forget such noble problems like anisotropic broadening. Last but not least : quantitative phase analysis by "Rietveld" is (when only scale factors are "on") nothing else but multiple linear regression. There is a huge volume of literature on the topic, especially which variables must, which should and which could be a part of your model. I really wonder why the authors of program do not add one option called "QUAN", which could, upon convergence of highly sophisticated non-linear L-S, fix all parameters but scale factors and run standard tests or factor analysis. One more diagonalization is not very time consuming, is it ? To avoid numerical problems, I'd use SVD. This idea is free and if it helps people reporting 0.1% MgO (SiO2) in a mixture of 10 phases to think a little of the numbers they are getting, I would only be happy :-) Lubo P.S. Hereby I declare I have never used Topas and I am thus not familiar with all its advantages or disadvantages compared to other codes. On Wed, 21 Mar 2007, Reinhard Kleeberg wrote: > Dear Leandro Bravo, > some comments below: > > Leandro Bravo schrieb: > > > > > In the refinement of chlorite minerals with well defined disordering > > (layers shifting by exactly b/3 along the three pseudohexagonal Y > > axis), you separate the peaks into k = 3.n (relative sharp, less > > intensive peak) and k 3.n (broadened or disappeared > > reflections). How did you determined this value k = 3.n and n = > > 0,1,2,3..., right? > > > The occurence of stacking faults along the pseudohexagonal Y axes causes > broadening of all reflections hkl with k unequal 3n (for example 110, > 020, 111..) whereas the reflections with k equal 3n remain unaffected > (001, 131, 060, 331...). This is clear from geometric conditions, and > can be seen in single crystal XRD (oscillation photographs, Weissenberg > photographs) as well in selected area electron diffraction patterns. The > fact is known for a long time, and published and discussed in standard > textbooks, for example *Brindley, G.W., Brown, G.: Crystal Structures > of Clay Minerals and their X-ray Identification. Mineralogical Society, > London, 1980.* > > > First, the chlorite refinement. > > > > In the first refinement of chlorite you used no disordering models and > > used ´´cell parameters`` and ´´occupation of octahedra``. So you > > refined the lattice parameters and the occupancy of all atoms? > > Yes, the lattice parameters. > Only the occupation/substitution of atoms with significant difference in > scattering power can be refined in powder diffraction. In case of > chlorites, the substitution Fe-Mg at the 4 octahedral positions can be > refined. > > > > > In the second refinement, you use na anisotropic line broadening ´´in > > the traditional way``. So you used a simple ellipsoidal model and/or > > spherical harmonics? > > > Simple ellipsoidal model, assuming very thiny platy crystals. But it was > clear that this model must fail, see above the known fact of disorder in > layer stacking. And from microscopy it is clear that the "crystals" are > much too large to produce significant line broadening from size effects. > You can see this for a lot of clay minerals: If the "ellipsoidal > crystallite shape" model would be ok, the 00l reflections would have the > broadest lines, and the 110, 020 and so on should be the sharpest ones. > But this is not true in practice, mostly the hkl are terribly broadenend > and smeared, but the 00l are still sharp. > > > The last refinement, describing a real structure. You used for the > > reflections k 3.n (broadened peaks) a ´´rod-like intensity > > distribution``, with the rod being projected by the cosine of the > > direction on the diffractogram. You used also the lenghts of the rods > > as a parameter, so as the dimension of the rods for 0k0 with k > > 3.n. I would like to know how did you ´´project`` these rods > > and use them in the refinement. > > > > For the k = 3.n reflections, you used an anisotropic broadening model > > (aniso crystallyte size) and and isotropic br
Re: Problems using TOPAS R (Rietveld refinement)
Dear Leandro Bravo, some comments below: Leandro Bravo schrieb: In the refinement of chlorite minerals with well defined disordering (layers shifting by exactly b/3 along the three pseudohexagonal Y axis), you separate the peaks into k = 3.n (relative sharp, less intensive peak) and k 3.n (broadened or disappeared reflections). How did you determined this value k = 3.n and n = 0,1,2,3..., right? The occurence of stacking faults along the pseudohexagonal Y axes causes broadening of all reflections hkl with k unequal 3n (for example 110, 020, 111..) whereas the reflections with k equal 3n remain unaffected (001, 131, 060, 331...). This is clear from geometric conditions, and can be seen in single crystal XRD (oscillation photographs, Weissenberg photographs) as well in selected area electron diffraction patterns. The fact is known for a long time, and published and discussed in standard textbooks, for example *Brindley, G.W., Brown, G.: Crystal Structures of Clay Minerals and their X-ray Identification. Mineralogical Society, London, 1980.* First, the chlorite refinement. In the first refinement of chlorite you used no disordering models and used ´´cell parameters`` and ´´occupation of octahedra``. So you refined the lattice parameters and the occupancy of all atoms? Yes, the lattice parameters. Only the occupation/substitution of atoms with significant difference in scattering power can be refined in powder diffraction. In case of chlorites, the substitution Fe-Mg at the 4 octahedral positions can be refined. In the second refinement, you use na anisotropic line broadening ´´in the traditional way``. So you used a simple ellipsoidal model and/or spherical harmonics? Simple ellipsoidal model, assuming very thiny platy crystals. But it was clear that this model must fail, see above the known fact of disorder in layer stacking. And from microscopy it is clear that the "crystals" are much too large to produce significant line broadening from size effects. You can see this for a lot of clay minerals: If the "ellipsoidal crystallite shape" model would be ok, the 00l reflections would have the broadest lines, and the 110, 020 and so on should be the sharpest ones. But this is not true in practice, mostly the hkl are terribly broadenend and smeared, but the 00l are still sharp. The last refinement, describing a real structure. You used for the reflections k 3.n (broadened peaks) a ´´rod-like intensity distribution``, with the rod being projected by the cosine of the direction on the diffractogram. You used also the lenghts of the rods as a parameter, so as the dimension of the rods for 0k0 with k 3.n. I would like to know how did you ´´project`` these rods and use them in the refinement. For the k = 3.n reflections, you used an anisotropic broadening model (aniso crystallyte size) and and isotropic broadening model (microstrain broadening). But you said that crystallite size is an isotropic line broadening in my kaolinite refinement and I should not use it. So I use or not the cry size? Yes, we used an "additional" ellipsoidal broadening in order to describe any potential "thinning" of the crystals. But this broadening model was not significant because the broadening was dominated by the stacking faults. A "microstrain" makes sense because of natural chlorits are sometimes zoned in their chemical composition and a distribution of the lattice constants may occur. In one of your mails you mentioned "crysize gave reasonable numbers with low error", and from that I assumed you looked only on the errors of the isotropic crysize as defined in Topas. You must know what model you did apply. But it is clear that any "crysize" model is inadequate to describe the line broadening of kaolinite. Now the kaolinite refinement. In the first refinement was used fixed atomic positions and a conventional anisotropic peak broadening. This conventional anisotropic peak broadening would be the simple ellipsoidal model and/or spherical harmonics?! Only ellipsoidal model, assuming a platy crystal shape, see above. Only for comparision. After that you use the introduced model of disorfering. Is this model the same of the chlorite (rods for k 3.n and microstrain broadening and anisotropic crystallite size? Not exactly the same like in chlorite, because the disorder in kaolinite is much more complicated like in chlorites. See also the textbook cited above, and extensive works of Plancon and Tchoubar. Thus, most of the natural kaolinites show stacking faults along b/3 as well as along a, and additional random faults. Thus, more broadening parameters had to be defined, and this is not completely perfect until now. See the presentation I sent you last week. Best regards Reinhard Kleeberg begin:vcard fn:Reinhard Kleeberg n:Kleeberg;Reinhard org;quoted-printable:TU Bergakademie Freiberg;Institut f=C3=BCr Mineralogie adr:;;Brennhausgasse 14;
RE: Problems using TOPAS R (Rietveld refinement)
Leandro I would suggest that you use an internal standard to get a handle on your sources of uncertainty. I would suggest Baikalox corundum CR1 - while I don't know its non-diffracting content, it is probably low. I would suggest that you use the technique outlined in Pratapa et. al. Powder Diffraction 13(3) 166-170, and measure the diffractometer constant, then look at the relationship between s (scale factor) and phase concentration. If you want more details, contact me directly. regards, Tony Raftery At 02:59 AM 18/03/2007, you wrote: My purpose is really quantification. And I´m getting erros of about 5% in each phase (in the quantification part). I´m using samples that I made by mixing calcite, dolomite and kaolinite (18, 55 and 26 or near it). It is valid to mix the sample with a known standard if you are analysing a unknown sample (quantitatively). But I´d like to know more about this method to determine the amount of amorphous content using a standard. I´m using now a beq. of 20 in all atoms, and they are fix. Could you discriminate each variable of the equation that you send to me?! prm b 0 scale_pks = Exp(-b />D_spacing^2) Does it give reasonable values!? Regards, Leandro From: "AlanCoelho" <[EMAIL PROTECTED]> Reply-To: rietveld_l@ill.fr To: Subject: RE: Problems using TOPAS R (Rietveld refinement) Date: Fri, 16 Mar 2007 09:56:33 +1100 Leandro Not sure what the purpose of your refinement is but if it's quantification then your results would probably be in error to a large extent. The references given by Alan Hewat and Lubo Smrcok is probably a good starting point. Data quality and model errors typically mean that atomic positions should not be refined for clays; especially for Kaolinite. Also, use a common beq value for all sites or take them from literature. A gobal beq could then be superimposed using something like prm b 0 scale_pks = Exp(-b / D_spacing^2);. For quantification try spiking the sample with a standard to determine the amorphous content. It is possible to get the peak shapes without changing peak intensities; if you need assistance then contact me off the list. Cheers Alan -Original Message- From: Leandro Bravo [ mailto:[EMAIL PROTECTED]] Sent: Friday, 16 March 2007 9:15 AM To: rietveld_l@ill.fr Subject: Re: Problems using TOPAS R (Rietveld refinement) Ok, I´m starting to have sucess in the kaolinite refinement, the quantification is giving me reasonable values. I´m refining the thermal factors, all the atoms positions in the kaolinite, the lattice parameters and the cystallite size. Lattice parameters and crystallite size are giving me very good numbers, with very low errors (about 0,09). In the thermal factors, I realized that alll of them tend to 20, so after all refinements I put them to 20, and refine all over again. I don´t care that much for atoms positions, I´m only using them because refining only lattice, thermal and cry size wasn´t enough to make a good calculated pattern to compare with the measured one. In the calcite and dolomite I refine: lattice parameters, cry size and thermal factors. And use on both a preferred orientation correction (spherical harmonics 4 th order). The RWP is about 16. I´d to hear some opinions about this strategy of refinement, if you think that I can spare some refining cycles or even fix some values to reduce erros in the refinement. _ Descubra como mandar Torpedos SMS do seu Messenger para o celular dos seus amigos. http://mobile.msn.com/ _ Descubra como mandar Torpedos do Messenger para o celular! http://mobile.msn.com/ Tony Raftery Senior Technologist AEMF & XAF, R Block Faculty of Science, GP Queensland University of Technology c/- AEMF, R Block Gardens Point Road, Brisbane, 4000 (or) GPO Box 2434 Brisbane 4001 AUSTRALIA ph +61 7 3138 2271 fax +61 7 3138 5100 email [EMAIL PROTECTED] http://www.xaf.qut.edu.au/ please note new phone number from 16/10/2006
Re: Problems using TOPAS R (Rietveld refinement)
Mr. Kleeberg, Read the paper that you send to me, ´´RIETVELD ANALYSIS OF DISORDERED LAYER SILICATES``, and I have some questions about it. In the refinement of chlorite minerals with well defined disordering (layers shifting by exactly b/3 along the three pseudohexagonal Y axis), you separate the peaks into k = 3.n (relative sharp, less intensive peak) and k 3.n (broadened or disappeared reflections). How did you determined this value k = 3.n and n = 0,1,2,3..., right? First, the chlorite refinement. In the first refinement of chlorite you used no disordering models and used ´´cell parameters`` and ´´occupation of octahedra``. So you refined the lattice parameters and the occupancy of all atoms? In the second refinement, you use na anisotropic line broadening ´´in the traditional way``. So you used a simple ellipsoidal model and/or spherical harmonics? The last refinement, describing a real structure. You used for the reflections k 3.n (broadened peaks) a ´´rod-like intensity distribution``, with the rod being projected by the cosine of the direction on the diffractogram. You used also the lenghts of the rods as a parameter, so as the dimension of the rods for 0k0 with k 3.n. I would like to know how did you ´´project`` these rods and use them in the refinement. For the k = 3.n reflections, you used an anisotropic broadening model (aniso crystallyte size) and and isotropic broadening model (microstrain broadening). But you said that crystallite size is an isotropic line broadening in my kaolinite refinement and I should not use it. So I use or not the cry size? Now the kaolinite refinement. In the first refinement was used fixed atomic positions and a conventional anisotropic peak broadening. This conventional anisotropic peak broadening would be the simple ellipsoidal model and/or spherical harmonics?! After that you use the introduced model of disorfering. Is this model the same of the chlorite (rods for k 3.n and microstrain broadening and anisotropic crystallite size? Thank you very much. Regards, Leandro _ Seja um dos primeiros a testar o novo Windows Live Mail Beta- grátis. Acesse http://www.ideas.live.com/programpage.aspx?versionId=5d21c51a-b161-4314-9b0e-4911fb2b2e6d
RE: Problems using TOPAS R (Rietveld refinement)
My purpose is really quantification. And I´m getting erros of about 5% in each phase (in the quantification part). I´m using samples that I made by mixing calcite, dolomite and kaolinite (18, 55 and 26 or near it). It is valid to mix the sample with a known standard if you are analysing a unknown sample (quantitatively). But I´d like to know more about this method to determine the amount of amorphous content using a standard. I´m using now a beq. of 20 in all atoms, and they are fix. Could you discriminate each variable of the equation that you send to me?! prm b 0 scale_pks = Exp(-b />D_spacing^2) Does it give reasonable values!? Regards, Leandro From: "AlanCoelho" <[EMAIL PROTECTED]> Reply-To: rietveld_l@ill.fr To: Subject: RE: Problems using TOPAS R (Rietveld refinement) Date: Fri, 16 Mar 2007 09:56:33 +1100 Leandro Not sure what the purpose of your refinement is but if it's quantification then your results would probably be in error to a large extent. The references given by Alan Hewat and Lubo Smrcok is probably a good starting point. Data quality and model errors typically mean that atomic positions should not be refined for clays; especially for Kaolinite. Also, use a common beq value for all sites or take them from literature. A gobal beq could then be superimposed using something like prm b 0 scale_pks = Exp(-b / D_spacing^2);. For quantification try spiking the sample with a standard to determine the amorphous content. It is possible to get the peak shapes without changing peak intensities; if you need assistance then contact me off the list. Cheers Alan -Original Message- From: Leandro Bravo [mailto:[EMAIL PROTECTED] Sent: Friday, 16 March 2007 9:15 AM To: rietveld_l@ill.fr Subject: Re: Problems using TOPAS R (Rietveld refinement) Ok, I´m starting to have sucess in the kaolinite refinement, the quantification is giving me reasonable values. I´m refining the thermal factors, all the atoms positions in the kaolinite, the lattice parameters and the cystallite size. Lattice parameters and crystallite size are giving me very good numbers, with very low errors (about 0,09). In the thermal factors, I realized that alll of them tend to 20, so after all refinements I put them to 20, and refine all over again. I don´t care that much for atoms positions, I´m only using them because refining only lattice, thermal and cry size wasn´t enough to make a good calculated pattern to compare with the measured one. In the calcite and dolomite I refine: lattice parameters, cry size and thermal factors. And use on both a preferred orientation correction (spherical harmonics 4 th order). The RWP is about 16. I´d to hear some opinions about this strategy of refinement, if you think that I can spare some refining cycles or even fix some values to reduce erros in the refinement. _ Descubra como mandar Torpedos SMS do seu Messenger para o celular dos seus amigos. http://mobile.msn.com/ _ Descubra como mandar Torpedos do Messenger para o celular! http://mobile.msn.com/
Re: Problems using TOPAS R (Rietveld refinement)
Dear Leandro, some comments: Leandro Bravo schrieb: I know that refining the atoms positions is ´´too much´´, exagerated. But is the only way I can make the calculated DRX pattern fit with the measured one. There must a problem in the instrument details since I´m using Fundamental Parameters (FP) for peak shape, the values I put in the instrument description play a major role in FP, am I right? No. The misfit in your Rietveld refinement of kaolinite you get by using published atomic coordinates and temperature factors does definitely not arise from wrong published structure date and probably not significantly from any error in your instrumental parameters. Kaolinite diffraction pattern can not be described by simple isotropic line broadening as you tried by the "crystallite size" parameter. The different types and amounts of stacking faults in kaolinite are the reason for different kinds of "smearing" of the reciprocal lattice points. It makes no sense to refine atomic coordinates and temperature factors in an ideal cell to get a better Rwp of a disordered structure: One will of course get a better fit, but this is reached by variations of intensity by meaningless atomic positions. I made a new scan, of the same sample, with range from 10° to 80°, step size 0,02 and count time 4 seconds. The old one was from 5° to 120,° maybe it is prejudicing the background refining. Tomorrow I´m gonna to scrap this old pattern and work with the new one. I´m having a good response refining the calcite and teh dolomite in the sample only refining lattice parameters, cry size and beq. I think that refining this is what we can call a ´´normal refining method``. Now the kaolinite... The major problem is that I have a sample from a laterite with hydroxyapatite, calcite, dolomite, vermiculite and other phases. The vermiculite is very alterated and in the DRX pattern we can confuse it with other ``layered silicates``, it will be a huge problem. But I will only put my hands on these samples after finishing with the kaolinite. "Altered vermiculite" is probably a mixed-layered clay mineral? If yes, I'm in doubt that you can quantify this by the Rietveld method. See: Omotoso, O., McCarty, D.K., Hillier, S., Kleeberg, R. (2006) Some successful approaches to quantitative mineral analysis as revealed by the 3^rd Reynolds Cup contest. Clays and Clay Minerals, 54 (6), 751-763. One question, these ´´models`` and ´´trials`` that you talk about regarding the kaolinite is used in the CIF part of the refinement, am I right?! It´s not a part of the TOPAS itself. right? I think he CIF part you are referring is from the database you used (ICSD), right? These data refer to the ideal cell. One must introduce any models regarding line broadening or supercell coordinates into your structure model (*.str ?) what is used in your refinement. You will not find such models in a crystallographic database, specific formulations are necessary, depending on your "disorder problem" and on the capabilities of your Rietveld program. Best regards Reinhard Thank you, Leandro _ Chegou o Windows Live Spaces com rede social. Confira http://spaces.live.com/ begin:vcard fn:Reinhard Kleeberg n:Kleeberg;Reinhard org;quoted-printable:TU Bergakademie Freiberg;Institut f=C3=BCr Mineralogie adr:;;Brennhausgasse 14;Freiberg;Sachsen;D-09596;Germany email;internet:[EMAIL PROTECTED] title:Dr. tel;work:(+49) (0)3731 393244 tel;fax:(+49)(0)3731 393129 url:http://www.mineral.tu-freiberg.de/mineralogie/roelabor/ version:2.1 end:vcard
RE: Problems using TOPAS R (Rietveld refinement)
I know that refining the atoms positions is ´´too much´´, exagerated. But is the only way I can make the calculated DRX pattern fit with the measured one. There must a problem in the instrument details since I´m using Fundamental Parameters (FP) for peak shape, the values I put in the instrument description play a major role in FP, am I right? I made a new scan, of the same sample, with range from 10° to 80°, step size 0,02 and count time 4 seconds. The old one was from 5° to 120,° maybe it is prejudicing the background refining. Tomorrow I´m gonna to scrap this old pattern and work with the new one. I´m having a good response refining the calcite and teh dolomite in the sample only refining lattice parameters, cry size and beq. I think that refining this is what we can call a ´´normal refining method``. Now the kaolinite... The major problem is that I have a sample from a laterite with hydroxyapatite, calcite, dolomite, vermiculite and other phases. The vermiculite is very alterated and in the DRX pattern we can confuse it with other ``layered silicates``, it will be a huge problem. But I will only put my hands on these samples after finishing with the kaolinite. One question, these ´´models`` and ´´trials`` that you talk about regarding the kaolinite is used in the CIF part of the refinement, am I right?! It´s not a part of the TOPAS itself. right? Thank you, Leandro _ Chegou o Windows Live Spaces com rede social. Confira http://spaces.live.com/
RE: Problems using TOPAS R (Rietveld refinement)
Leandro Not sure what the purpose of your refinement is but if it's quantification then your results would probably be in error to a large extent. The references given by Alan Hewat and Lubo Smrcok is probably a good starting point. Data quality and model errors typically mean that atomic positions should not be refined for clays; especially for Kaolinite. Also, use a common beq value for all sites or take them from literature. A gobal beq could then be superimposed using something like prm b 0 scale_pks = Exp(-b / D_spacing^2);. For quantification try spiking the sample with a standard to determine the amorphous content. It is possible to get the peak shapes without changing peak intensities; if you need assistance then contact me off the list. Cheers Alan -Original Message- From: Leandro Bravo [mailto:[EMAIL PROTECTED] Sent: Friday, 16 March 2007 9:15 AM To: rietveld_l@ill.fr Subject: Re: Problems using TOPAS R (Rietveld refinement) Ok, I´m starting to have sucess in the kaolinite refinement, the quantification is giving me reasonable values. I´m refining the thermal factors, all the atoms positions in the kaolinite, the lattice parameters and the cystallite size. Lattice parameters and crystallite size are giving me very good numbers, with very low errors (about 0,09). In the thermal factors, I realized that alll of them tend to 20, so after all refinements I put them to 20, and refine all over again. I don´t care that much for atoms positions, I´m only using them because refining only lattice, thermal and cry size wasn´t enough to make a good calculated pattern to compare with the measured one. In the calcite and dolomite I refine: lattice parameters, cry size and thermal factors. And use on both a preferred orientation correction (spherical harmonics 4 th order). The RWP is about 16. I´d to hear some opinions about this strategy of refinement, if you think that I can spare some refining cycles or even fix some values to reduce erros in the refinement. _ Descubra como mandar Torpedos SMS do seu Messenger para o celular dos seus amigos. http://mobile.msn.com/
RE: Re: Problems using TOPAS R (Rietveld refinement)
Leandro, You probably should consult the references suggested by Alan Hewat and Reinhard Kleeberg before you read anything into your "reasonable" Rwp. Kaolinite is grossly over-parametized in your refinement strategy. If you are stuck with TOPAS, you may want to contact Arnt Kern (Bruker) about last year's TOPAS workshop. I recall that there was a paper on refinement strategies for disordered clays. Dipo Omotoso CANMET Energy Technology Centre - Devon Energy Technology and Programs Sector Natural Resources Canada #1 Oil Patch Drive, Devon, AB. Canada Groupe des techniques perfectionnées de séparation Centre de la technologie de l'énergie de CANMET - Devon Secteur de la technologie et des programmes de l'énergie Ressources naturelles Canada -Original Message- From: Leandro Bravo [mailto:[EMAIL PROTECTED] Sent: Thursday, March 15, 2007 4:15 PM To: rietveld_l@ill.fr Subject: Re: Problems using TOPAS R (Rietveld refinement) Ok, I´m starting to have sucess in the kaolinite refinement, the quantification is giving me reasonable values. I´m refining the thermal factors, all the atoms positions in the kaolinite, the lattice parameters and the cystallite size. Lattice parameters and crystallite size are giving me very good numbers, with very low errors (about 0,09). In the thermal factors, I realized that alll of them tend to 20, so after all refinements I put them to 20, and refine all over again. I don´t care that much for atoms positions, I´m only using them because refining only lattice, thermal and cry size wasn´t enough to make a good calculated pattern to compare with the measured one. In the calcite and dolomite I refine: lattice parameters, cry size and thermal factors. And use on both a preferred orientation correction (spherical harmonics 4 th order). The RWP is about 16. I´d to hear some opinions about this strategy of refinement, if you think that I can spare some refining cycles or even fix some values to reduce erros in the refinement. _ Descubra como mandar Torpedos SMS do seu Messenger para o celular dos seus amigos. http://mobile.msn.com/
Re: Problems using TOPAS R (Rietveld refinement)
Ok, I´m starting to have sucess in the kaolinite refinement, the quantification is giving me reasonable values. I´m refining the thermal factors, all the atoms positions in the kaolinite, the lattice parameters and the cystallite size. Lattice parameters and crystallite size are giving me very good numbers, with very low errors (about 0,09). In the thermal factors, I realized that alll of them tend to 20, so after all refinements I put them to 20, and refine all over again. I don´t care that much for atoms positions, I´m only using them because refining only lattice, thermal and cry size wasn´t enough to make a good calculated pattern to compare with the measured one. In the calcite and dolomite I refine: lattice parameters, cry size and thermal factors. And use on both a preferred orientation correction (spherical harmonics 4 th order). The RWP is about 16. I´d to hear some opinions about this strategy of refinement, if you think that I can spare some refining cycles or even fix some values to reduce erros in the refinement. _ Descubra como mandar Torpedos SMS do seu Messenger para o celular dos seus amigos. http://mobile.msn.com/
Re: Problems using TOPAS R (Rietveld refinement)
Thanks Alan, our first trial was: Bergmann, J., Kleeberg, R. (1998) Rietveld analysis of disordered layer silicates. Mat. Sci. Forum, 278-281 (1): 300-305. Application to kaolinite at: http://www.bgmn.de/kaolin.html and for more disordered stuff: http://www.bgmn.de/smectite.html Far from beeing perfect, but sometimes working in quantification... Reinhard Alan Hewat schrieb: Reinhard Kleeberg said: There are not so much trials published to find a working solution for practical Rietveld quantification of clays. One would be a self-citation of a paper, so I can't do this here in the list. A good one is :-) Pitfalls in Rietveld Phase Quantification of Complex Samples R. Kleeberg (2005) Microstructure Analysis in Materials Science http://www.ww.tu-freiberg.de/mk/bht/Abstracts/kleeberg.pdf _ Dr Alan Hewat, ILL Grenoble, FRANCE <[EMAIL PROTECTED]>fax+33.476.20.76.48 +33.476.20.72.13 (.26 Mme Guillermet) http://www.ill.fr/dif/people/hewat/ _ begin:vcard fn:Reinhard Kleeberg n:Kleeberg;Reinhard org;quoted-printable:TU Bergakademie Freiberg;Institut f=C3=BCr Mineralogie adr:;;Brennhausgasse 14;Freiberg;Sachsen;D-09596;Germany email;internet:[EMAIL PROTECTED] title:Dr. tel;work:(+49) (0)3731 393244 tel;fax:(+49)(0)3731 393129 url:http://www.mineral.tu-freiberg.de/mineralogie/roelabor/ version:2.1 end:vcard
Re: Problems using TOPAS R (Rietveld refinement)
Or, to see how bad the results from Rietveld refinements of kaolintes are try review paper in Zeitschrift fuer Kristallographie 210(3) 177-183, 1997 lubo smrcok On Wed, 14 Mar 2007, Alan Hewat wrote: > Reinhard Kleeberg said: > > There are not so much trials published to find a > > working solution for practical Rietveld quantification of clays. One > > would be a self-citation of a paper, so I can't do this here in the list. > > A good one is :-) > > Pitfalls in Rietveld Phase Quantification of Complex Samples > R. Kleeberg (2005) Microstructure Analysis in Materials Science > http://www.ww.tu-freiberg.de/mk/bht/Abstracts/kleeberg.pdf > _ > Dr Alan Hewat, ILL Grenoble, FRANCE <[EMAIL PROTECTED]>fax+33.476.20.76.48 > +33.476.20.72.13 (.26 Mme Guillermet) http://www.ill.fr/dif/people/hewat/ > _ > >
Re: Problems using TOPAS R (Rietveld refinement)
Reinhard Kleeberg said: > There are not so much trials published to find a > working solution for practical Rietveld quantification of clays. One > would be a self-citation of a paper, so I can't do this here in the list. A good one is :-) Pitfalls in Rietveld Phase Quantification of Complex Samples R. Kleeberg (2005) Microstructure Analysis in Materials Science http://www.ww.tu-freiberg.de/mk/bht/Abstracts/kleeberg.pdf _ Dr Alan Hewat, ILL Grenoble, FRANCE <[EMAIL PROTECTED]>fax+33.476.20.76.48 +33.476.20.72.13 (.26 Mme Guillermet) http://www.ill.fr/dif/people/hewat/ _
Re: Problems using TOPAS R (Rietveld refinement)
Leandro, the refinement/profile fitting of kaolinite-bearing samples is strongly affected by disorder of natural kaolinites. The atomic coordinates in ICSD (for example Bish and von Dreele) have been derived from the best ordered samples known on earth, mainly Keokuk site. "Real-world" kaolinites from deposits are disordered by several types of stacking faults, see the textbook Brindley, G.W. (Ed.) Crystal structures of clay minerals and their X-ray identification. Mineralogical Society, London, 1980. see several detailed works done by Alan Plancon, and a very good general treatment Drits, V.A. and Tchoubar, C. X-ray diffraction by disordered lamellar structures. Springer, 1990 ISBN 3-540-51222-5 Thus, Rietveld refinement of such structures needs for a model what can treat the "anisotropic line broadening" and all the other diffraction effects caused by the stacking faults. Until now, no general model suitable for Rietveld refinement of all varieties of disorder in kaolinite does exist. There are not so much trials published to find a working solution for practical Rietveld quantification of clays. One would be a self-citation of a paper, so I can't do this here in the list. Nevertheless, even with the best models available you will not be able to refine "true" temperature factors of kaolinite from powder data of disordered kaolinites. I would recommend to keep the temperature factors fixed in phase quantification work, and to think about a "reasonable" model for the description of disorder in your actual kaolinite. Reinhard Leandro Bravo schrieb: Ok... another problem... I don´t think that the kaolinite CIF that I´m using is working well, I´m refining the temperature factors and it´s giving me non realistic numbers. Can somebody send me a trustable kaolinite CIF, with good temperature factors?! Other doubt... I´m making my scans from 5 (2-theta) to 120 (2-theta), and I´m realizing that above 80° I´m getting unecessary data (basically just backgorund). The question is how this ´´unecessary data`` affect the quantification?!?! From: "Leandro Bravo" <[EMAIL PROTECTED]> Reply-To: rietveld_l@ill.fr To: rietveld_l@ill.fr Subject: Re: Problems using TOPAS R (Rietveld refinement) Date: Mon, 12 Mar 2007 13:35:54 -0300 I think that I just did a good job in my quantification: 50,2% calcite and 49,8% dolomite. Now I´m moving foward to a sinthetic mixture of calcite, dolomite and kaolinite. I have other questin, how can I determine a trustable value to the Full Axial Model?! Especially the these paramters: sample lenght, source lenght and RS lenght?!?! I´m starting to realize that the temperature factors are the key to the refinement! They change the calculated pattern so much!!! From: "jilin_zhang_Houston" <[EMAIL PROTECTED]> Reply-To: rietveld_l@ill.fr To: "rietveld_l@ill.fr" Subject: Re: Problems using TOPAS R (Rietveld refinement) Date: Mon, 12 Mar 2007 10:39:41 -0600 Leandro : here is an example of calcite I used. You can use min and max to confine the parameters. One way to know whether it is right is to mix a known fraction of a compound, e.g. ZnO with a ratio of original sample/ZnO=100/15. At the end of the refinement, you have N components with N corrected(with volume and density) scalefactor, S(i), Weight(i)=S(i)/S(ZnO)*15 the sum of all weight(i) should be close to 100 if the whole thing is crystalline. str phase_name calcite scale sc_calcite 0.0001813894308 space_group R-3c r_bragg 5.769971925 Crystallite_Size(cs_calcite, 100 min =100; max =1000;) Trigonal(a_calcite 4.995096119 min =4.95; max =5.2;,c_calcite 17.08621648 min =16.9; max =17.1;) site Ca num_posns 6 x 0 y 0 z 0 occ Ca+2 1 beq 0.95 site C num_posns 6 x 0 y 0 z =1/4; : 0.25 occ C 1 beq 0.9 site O1 num_posns 18 x 0.257 y 0 z =1/4; : 0.25 occ O-2 1 beq 0.94 PO_Spherical_Harmonics(sh_calcite, 2 ) Cheers J Hi, guys, I´m having some trouble using the Bruker software TOPAS R, right now I´m quantifying a sinthetic sample with 50% of calcite and 50% of dolomite. Check the following questions an help me if you can. 1) I´m using the CIF files from ICSD, but when I put it in the software it gives me a temperature factor (beq.) of 1. Is there anyway I can check some good temperature factors?! When i put then to refine, sometimes they become negative, but the calculated - observed pattern is just good. 2) I´m using Fundamental Paramaters and for these I must have acknowledge of my instrument, well I have, minus sample lenght... and stuff like that... is there anyway I can determine these values with accuacy and use them with sure?! 3) In TOPAS how do I know if the refinement is good?! Because each time I refine the 50%/50% mixture I have different results and I don´t know wich one gives me a result that I can trust. Thank ou in advance, Lean
Re: Problems using TOPAS R (Rietveld refinement)
Leandro Bravo said: > I don´t think that the kaolinite CIF that I´m using is working well, I´m > refining the temperature factors and it´s giving me non realistic numbers. > Can somebody send me a trustable kaolinite CIF, with good temperature > factors?! You will find a dozen papers on the structure of kaolinite in ICSD. You should be able to download for free the ones in Clays and Clay Minerals by constructing URLs like this: http://www.crossref.org/openurl?aulast=Neder&title=Clays%20and%20Clay%20Minerals&volume=47&spage=487&year=1999 > Other doubt... I´m making my scans from 5 (2-theta) to 120 (2-theta), and > I´m realizing that above 80° I´m getting unecessary data (basically just > backgorund). The question is how this ´´unecessary data`` affect the > quantification?!?! I guess you may well have trouble refining realistic temperature factors if you are also refining the background and you can see no peaks above 80°. Clays are often not well ordered. You can't blame TOPAS or the CIF for that :-) Try fixing the background and/or temperature factors. Neder, R.B.;Burghammer, M.;Grasl, T.;Schulz, H.;Bram, A.;Fiedler, S. Refinement of the kaolinite structure from single-crystal synchrotron data (1999) Clays and Clay Minerals 47, 487-494 Akiba, E.; Hayakawa, H.; Hayashi, S.; Miyawaki, R.; Tomura, S.; Shibasaki, Y.; Izumi, F.; Asano, H.; Kamiyama, T. Structure refinement of synthetic deuterated kaolinite by Rietveld analysis using time-of-flight neutron powder diffraction data (1997) Clays and Clay Minerals 45, 781-788 Bish, D.L. Rietveld refinement of the kaolinite structure at 1.5K (1993) Clays and Clay Minerals 41, 738-744 Bish, D.L.;von Dreele, R.B. Rietveld refinement of non-hydrogen atomic positions in kaolinite (1989) Clays and Clay Minerals 37, 289-296 Young, R.A.;Hewat, A.W. Verification of the Triclinic Crystal Structure of Kaolinite (1988) Clays and Clay Minerals 36, 225-232 _ Dr Alan Hewat, ILL Grenoble, FRANCE <[EMAIL PROTECTED]>fax+33.476.20.76.48 +33.476.20.72.13 (.26 Mme Guillermet) http://www.ill.fr/dif/people/hewat/ _
Re: Problems using TOPAS R (Rietveld refinement)
Ok... another problem... I don´t think that the kaolinite CIF that I´m using is working well, I´m refining the temperature factors and it´s giving me non realistic numbers. Can somebody send me a trustable kaolinite CIF, with good temperature factors?! Other doubt... I´m making my scans from 5 (2-theta) to 120 (2-theta), and I´m realizing that above 80° I´m getting unecessary data (basically just backgorund). The question is how this ´´unecessary data`` affect the quantification?!?! From: "Leandro Bravo" <[EMAIL PROTECTED]> Reply-To: rietveld_l@ill.fr To: rietveld_l@ill.fr Subject: Re: Problems using TOPAS R (Rietveld refinement) Date: Mon, 12 Mar 2007 13:35:54 -0300 I think that I just did a good job in my quantification: 50,2% calcite and 49,8% dolomite. Now I´m moving foward to a sinthetic mixture of calcite, dolomite and kaolinite. I have other questin, how can I determine a trustable value to the Full Axial Model?! Especially the these paramters: sample lenght, source lenght and RS lenght?!?! I´m starting to realize that the temperature factors are the key to the refinement! They change the calculated pattern so much!!! From: "jilin_zhang_Houston" <[EMAIL PROTECTED]> Reply-To: rietveld_l@ill.fr To: "rietveld_l@ill.fr" Subject: Re: Problems using TOPAS R (Rietveld refinement) Date: Mon, 12 Mar 2007 10:39:41 -0600 Leandro : here is an example of calcite I used. You can use min and max to confine the parameters. One way to know whether it is right is to mix a known fraction of a compound, e.g. ZnO with a ratio of original sample/ZnO=100/15. At the end of the refinement, you have N components with N corrected(with volume and density) scalefactor, S(i), Weight(i)=S(i)/S(ZnO)*15 the sum of all weight(i) should be close to 100 if the whole thing is crystalline. str phase_name calcite scale sc_calcite 0.0001813894308 space_group R-3c r_bragg 5.769971925 Crystallite_Size(cs_calcite, 100 min =100; max =1000;) Trigonal(a_calcite 4.995096119 min =4.95; max =5.2;,c_calcite 17.08621648 min =16.9; max =17.1;) site Ca num_posns 6 x 0 y 0 z 0 occ Ca+2 1 beq 0.95 site C num_posns 6 x 0 y 0 z =1/4; : 0.25 occ C 1 beq 0.9 site O1 num_posns 18 x 0.257 y 0 z =1/4; : 0.25 occ O-2 1 beq 0.94 PO_Spherical_Harmonics(sh_calcite, 2 ) Cheers J Hi, guys, I´m having some trouble using the Bruker software TOPAS R, right now I´m quantifying a sinthetic sample with 50% of calcite and 50% of dolomite. Check the following questions an help me if you can. 1) I´m using the CIF files from ICSD, but when I put it in the software it gives me a temperature factor (beq.) of 1. Is there anyway I can check some good temperature factors?! When i put then to refine, sometimes they become negative, but the calculated - observed pattern is just good. 2) I´m using Fundamental Paramaters and for these I must have acknowledge of my instrument, well I have, minus sample lenght... and stuff like that... is there anyway I can determine these values with accuacy and use them with sure?! 3) In TOPAS how do I know if the refinement is good?! Because each time I refine the 50%/50% mixture I have different results and I don´t know wich one gives me a result that I can trust. Thank ou in advance, Leandro Bravo Ferreira da Costa Student, UFRJ - Universidade Federal do Rio de Janeiro - BR CETEM - RJ _ Inscreva-se no novo Windows Live Mail beta e seja um dos primeiros a testar as novidades-grátis. Saiba mais: http://www.ideas.live.com/programpage.aspx?versionId=5d21c51a-b161-4314-9b0e-4911fb2b2e6d _ Seja um dos primeiros a testar o novo Windows Live Mail Beta- grátis. Acesse http://www.ideas.live.com/programpage.aspx?versionId=5d21c51a-b161-4314-9b0e-4911fb2b2e6d _ Verificador de Segurança do Windows Live OneCare: combata já vírus e outras ameaças! http://onecare.live.com/site/pt-br/default.htm
Re: Problems using TOPAS R (Rietveld refinement)
I think that I just did a good job in my quantification: 50,2% calcite and 49,8% dolomite. Now I´m moving foward to a sinthetic mixture of calcite, dolomite and kaolinite. I have other questin, how can I determine a trustable value to the Full Axial Model?! Especially the these paramters: sample lenght, source lenght and RS lenght?!?! I´m starting to realize that the temperature factors are the key to the refinement! They change the calculated pattern so much!!! From: "jilin_zhang_Houston" <[EMAIL PROTECTED]> Reply-To: rietveld_l@ill.fr To: "rietveld_l@ill.fr" Subject: Re: Problems using TOPAS R (Rietveld refinement) Date: Mon, 12 Mar 2007 10:39:41 -0600 Leandro : here is an example of calcite I used. You can use min and max to confine the parameters. One way to know whether it is right is to mix a known fraction of a compound, e.g. ZnO with a ratio of original sample/ZnO=100/15. At the end of the refinement, you have N components with N corrected(with volume and density) scalefactor, S(i), Weight(i)=S(i)/S(ZnO)*15 the sum of all weight(i) should be close to 100 if the whole thing is crystalline. str phase_name calcite scale sc_calcite 0.0001813894308 space_group R-3c r_bragg 5.769971925 Crystallite_Size(cs_calcite, 100 min =100; max =1000;) Trigonal(a_calcite 4.995096119 min =4.95; max =5.2;,c_calcite 17.08621648 min =16.9; max =17.1;) site Ca num_posns 6 x 0 y 0 z 0 occ Ca+2 1 beq 0.95 site C num_posns 6 x 0 y 0 z =1/4; : 0.25 occ C 1 beq 0.9 site O1 num_posns 18 x 0.257 y 0 z =1/4; : 0.25 occ O-2 1 beq 0.94 PO_Spherical_Harmonics(sh_calcite, 2 ) Cheers J Hi, guys, I´m having some trouble using the Bruker software TOPAS R, right now I´m quantifying a sinthetic sample with 50% of calcite and 50% of dolomite. Check the following questions an help me if you can. 1) I´m using the CIF files from ICSD, but when I put it in the software it gives me a temperature factor (beq.) of 1. Is there anyway I can check some good temperature factors?! When i put then to refine, sometimes they become negative, but the calculated - observed pattern is just good. 2) I´m using Fundamental Paramaters and for these I must have acknowledge of my instrument, well I have, minus sample lenght... and stuff like that... is there anyway I can determine these values with accuacy and use them with sure?! 3) In TOPAS how do I know if the refinement is good?! Because each time I refine the 50%/50% mixture I have different results and I don´t know wich one gives me a result that I can trust. Thank ou in advance, Leandro Bravo Ferreira da Costa Student, UFRJ - Universidade Federal do Rio de Janeiro - BR CETEM - RJ _ Inscreva-se no novo Windows Live Mail beta e seja um dos primeiros a testar as novidades-grátis. Saiba mais: http://www.ideas.live.com/programpage.aspx?versionId=5d21c51a-b161-4314-9b0e-4911fb2b2e6d _ Seja um dos primeiros a testar o novo Windows Live Mail Beta- grátis. Acesse http://www.ideas.live.com/programpage.aspx?versionId=5d21c51a-b161-4314-9b0e-4911fb2b2e6d
Re: Problems using TOPAS R (Rietveld refinement)
Leandro : here is an example of calcite I used. You can use min and max to confine the parameters. One way to know whether it is right is to mix a known fraction of a compound, e.g. ZnO with a ratio of original sample/ZnO=100/15. At the end of the refinement, you have N components with N corrected(with volume and density) scalefactor, S(i), Weight(i)=S(i)/S(ZnO)*15 the sum of all weight(i) should be close to 100 if the whole thing is crystalline. str phase_name calcite scale sc_calcite 0.0001813894308 space_group R-3c r_bragg 5.769971925 Crystallite_Size(cs_calcite, 100 min =100; max =1000;) Trigonal(a_calcite 4.995096119 min =4.95; max =5.2;,c_calcite 17.08621648 min =16.9; max =17.1;) site Ca num_posns 6 x 0 y 0 z 0 occ Ca+2 1 beq 0.95 site C num_posns 6 x 0 y 0 z =1/4; : 0.25 occ C 1 beq 0.9 site O1 num_posns 18 x 0.257 y 0 z =1/4; : 0.25 occ O-2 1 beq 0.94 PO_Spherical_Harmonics(sh_calcite, 2 ) Cheers J Hi, guys, I´m having some trouble using the Bruker software TOPAS R, right now I´m quantifying a sinthetic sample with 50% of calcite and 50% of dolomite. Check the following questions an help me if you can. 1) I´m using the CIF files from ICSD, but when I put it in the software it gives me a temperature factor (beq.) of 1. Is there anyway I can check some good temperature factors?! When i put then to refine, sometimes they become negative, but the calculated - observed pattern is just good. 2) I´m using Fundamental Paramaters and for these I must have acknowledge of my instrument, well I have, minus sample lenght... and stuff like that... is there anyway I can determine these values with accuacy and use them with sure?! 3) In TOPAS how do I know if the refinement is good?! Because each time I refine the 50%/50% mixture I have different results and I don´t know wich one gives me a result that I can trust. Thank ou in advance, Leandro Bravo Ferreira da Costa Student, UFRJ - Universidade Federal do Rio de Janeiro - BR CETEM - RJ _ Inscreva-se no novo Windows Live Mail beta e seja um dos primeiros a testar as novidades-grátis. Saiba mais: http://www.ideas.live.com/programpage.aspx?versionId=5d21c51a-b161-4314-9b0e-4911fb2b2e6d
Problems using TOPAS R (Rietveld refinement)
Hi, guys, I´m having some trouble using the Bruker software TOPAS R, right now I´m quantifying a sinthetic sample with 50% of calcite and 50% of dolomite. Check the following questions an help me if you can. 1) I´m using the CIF files from ICSD, but when I put it in the software it gives me a temperature factor (beq.) of 1. Is there anyway I can check some good temperature factors?! When i put then to refine, sometimes they become negative, but the calculated - observed pattern is just good. 2) I´m using Fundamental Paramaters and for these I must have acknowledge of my instrument, well I have, minus sample lenght... and stuff like that... is there anyway I can determine these values with accuacy and use them with sure?! 3) In TOPAS how do I know if the refinement is good?! Because each time I refine the 50%/50% mixture I have different results and I don´t know wich one gives me a result that I can trust. Thank ou in advance, Leandro Bravo Ferreira da Costa Student, UFRJ - Universidade Federal do Rio de Janeiro - BR CETEM - RJ _ Inscreva-se no novo Windows Live Mail beta e seja um dos primeiros a testar as novidades-grátis. Saiba mais: http://www.ideas.live.com/programpage.aspx?versionId=5d21c51a-b161-4314-9b0e-4911fb2b2e6d
Rietveld refinement training course
Dear Colleague,The PCG/SCMP (Physical Crystallography Group of the BritishCrystallographic Association/Structural Condensed Matter Physics groupof the Institute of Physics) will be holding a 3 day Rietveld refinementtraining course at the University of Durham , 7-10th of January 2007..The course is aimed at those relatively new to the technique and willinvolve a combination of lectures and extensive hands-on practicals.More details and online application can be found at:http://www.dur.ac.uk/john.evans/webpages/pcg_rietveld_school_2007.htmhttp://www.dur.ac.uk/john.evans/webpages/riet_register.htmThe application deadline is 20th November. Places are limited so please apply early.John EvansIvana EvansJeremy Cockcroft On behalf of the PCG/SCMP group Dr. Ivana Radosavljevic Evans Academic Fellow in Structural/Materials Chemistry Department of Chemistry University of Durham Science Site Durham DH1 3LE, U.K. Office: CY 244 Phone: (0191) 334-2594 Fax: (0191) 384-4737 www.dur.ac.uk/ivana.radosavljevic
Rietveld refinement for Alloys
Dear All, I am mainly dealing with metallic alloys. In most of the cases the alloying element is very less (2%-5%, weight) and are not detected by XRD. In this situation how to do Reitveld refinement of the XRD pattern from these alloys. If I perform Rieteveld refinement only giving the information for the Matrix (main element) I donot get good result. Please suggest what should I do to get better results. With best regards, Apu /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/ Apu Sarkar Research Fellow Variable Energy Cyclotron Centre Kolkata 700 064 phone: 91-33-2337-1230 (extn. 3190) Fax: 91-33-2334-6871 INDIA /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
Re: Size distribution from Rietveld refinement
Directly the distributions (both) using Fourier Transform (an FFT). Sufficiently fast, implementing it the correct way. Luca On Nov 24, 2004, at 12:14, Leonid Solovyov wrote: actually I implemented the size and strain distributions (both) in my Rietveld code (Maud) and I demoed it in Praha beginning of September Good news! I look forward to see the program. Which profile function do you use for size distribution analysis? Hopefully not TCH pseudo-Voigt... Regards, Leonid __ Do you Yahoo!? All your favorites on one personal page Try My Yahoo! http://my.yahoo.com
Re: Size distribution from Rietveld refinement
>actually I implemented the size and strain distributions (both) in my >Rietveld code (Maud) and I demoed it in Praha beginning of September Good news! I look forward to see the program. Which profile function do you use for size distribution analysis? Hopefully not TCH pseudo-Voigt... Regards, Leonid __ Do you Yahoo!? All your favorites on one personal page Try My Yahoo! http://my.yahoo.com
Re: Size distribution from Rietveld refinement
> actually I implemented the size and strain distributions (both) in my > Rietveld code (Maud) and I demoed it in Praha beginning of September. Thanks Luca, I'm very, very happy to hear that. Really you are moving very fast! I was prepared to come in Prague but, unfortunately, I had to cancel one week before from an unexpected family problem. Keep in touch. Best wishes, Nicolae Popa
Re: Size distribution from Rietveld refinement
True Nick, actually I implemented the size and strain distributions (both) in my Rietveld code (Maud) and I demoed it in Praha beginning of September. Actually the program was not released and it is still under testing because I changed also the interface and other parts that needed more work; but this new version will be ready soon for the public. Indeed I tried the size and strain distributions model on some samples and on the SSRR data. In some cases it does not really matter using distributions respect to other mathematical functions, but in few cases I got a dramatic improvement in the fitting with the distributions method. Residuals become flat! Rw really low. I hope to get a version ready for the public in one or two weeks, not too much work to do, but not too much time also, so everyone willing to try it can do it. Actually I forgot to mention, for who does not know it, Maud already contains also anisotropic size and microstrain (Popa model ;-)) ) and the size-strain part is separated from the instrumental broadening as it should be for size-strain analysis. The distributions and anisotropy models can be used together also. best regards, Luca Lutterotti On Nov 23, 2004, at 10:08, Nicolae Popa wrote: Good answer Davor, but why you are avoiding to say that if the size profile (15a, 21, 22) from JAC(2002)35, 338-346 (used in 3.1 of RR paper) would be implemented in the Rietveld codes these codes would become much "powerful" and with a wider application in the size distribution determination? Nicolae
Re: Size distribution from Rietveld refinement
> gamma, or whatever we assume it to be. On the former, it is easy to see if
> observed profiles can't be successfully fit ("super-Lorentzian" peak
shapes,
> for instance), which means that the TCH peak shape cannot be used.
However,
> an assumption that physically broadened profiles (size and strain) are
also
> Voigt function is more difficult to prove; if not and one uses the
equations
> described above, a systematic error will be introduced. On the latter, a
Good answer Davor, but why you are avoiding to say that if the size profile
(15a, 21, 22) from JAC(2002)35, 338-346 (used in 3.1 of RR paper) would be
implemented in the Rietveld codes these codes would become much "powerful"
and with a wider application in the size distribution determination?
Nicolae
RE: Size distribution from Rietveld refinement
Thank you, Davor! Despite several HOWEVERs in your message it clarifies the situation. Best wishes, Leonid __ Do you Yahoo!? Meet the all-new My Yahoo! - Try it today! http://my.yahoo.com
RE: Size distribution from Rietveld refinement
Yes, one can determine size distribution parameters by using Rietveld
refinement. In particular, the lognormal size distribution is defined by two
parameters (say, the average radius and the distribution dispersion, see,
for instance, (2) and (3) of JAC 37 (2004) 911, SSRR for short here, or
other references therein). It was first shown by Krill & Birringer that both
volume-weighted (Dv) and area-weighted (Da) domain size (that are normally
evaluated in a diffraction experiment) can be related to the average radius
and dispersion of the lognormal distribution; one obtains something like (5)
in the paper SSRR. Therefore, if one can evaluate both Dv and Da by Rietveld
refinement, it would be possible to determine the parameters of the size
distribution, as two independent parameters are required to define the
lognormal or similar types of bell-shaped distributions. Note here that a
different distribution can be used, which will change the relationship
between Dv & Da and the parameters of the distribution (for the gamma
distribution, see JAC 35 (2002) 338, for the equations equivalent to (5) in
SSRR). The value that is normally evaluated through the Rietveld refinement
is Dv, as the refinable parameters in the Thompson-Cox-Hastings (TCH) model
are based on the integral-breadth methods. This means that one would have to
use (9) and (15)-(18) in SSRR, to obtain Dv, which depends on both P and X
parameters. As the TCH model implicitly assumes Voigt functions for both
size and strain-broadened profiles ("double-Voigt" model), Da can be also
calculated, but from X only, as it depends only on the Lorentzian
size-broadened integral breadth, Da=1/(2betaL) (this and other consequences
of a "double-Voigt" model were shown/discussed in JAC 26 (1993) 97).
HOWEVER, as pointed out by others in previous messages, this assumes that
(i) Both observed and physically broadened profiles are Voigt functions,
which is implicit to the TCH model; (ii) Size distribution is lognormal,
gamma, or whatever we assume it to be. On the former, it is easy to see if
observed profiles can't be successfully fit ("super-Lorentzian" peak shapes,
for instance), which means that the TCH peak shape cannot be used. However,
an assumption that physically broadened profiles (size and strain) are also
Voigt function is more difficult to prove; if not and one uses the equations
described above, a systematic error will be introduced. On the latter, a
good fit in Rietveld means only that a lognormal or other assumed
distribution is one POSSIBLE approximation of the real size distribution in
the sample. However, this equally applies to all the other parameters
obtained through the Rietveld refinement and is not a special deficiency of
this model. Second, even if one obtains more information about the actual
size distribution via TEM, SEM, etc., sometimes it is very difficult to
discern between different bell-shaped size distributions, especially if the
size distribution is narrow.
Davor
Davor Balzar
Department of Physics & Astronomy
University of Denver
2112 E Wesley Ave
Denver, CO 80208
Phone: 303-871-2137
Fax: 303-871-4405
Web: www.du.edu/~balzar
National Institute of Standards and Technology (NIST)
Division 853
Boulder, CO 80305
Phone: 303-497-3006
Fax: 303-497-5030
Web: www.boulder.nist.gov/div853/balzar
> -Original Message-
> From: Leonid Solovyov [mailto:[EMAIL PROTECTED]
> Sent: Monday, November 22, 2004 3:12 AM
> To: [EMAIL PROTECTED]
> Subject: Size distribution from Rietveld refinement
>
> Dear Rietvelders,
>
> Despite the heated discussion of the problem, the initial question,
> which, actually, concerned the size distribution from Rietveld
> refinement, seems to be unsettled.
> Can we derive ANY information on the crystallite size distribution
> (based on sensible assumptions) from the Thompson-Cox-Hastings
> size-broadening parameters P and X normally obtained from Rietveld
> refinement?
> For the Ceria Size-Strain Round Robin sample the crystallite
> distribution dispersion was determined from the profile analysis
> assuming lognormal distribution. This suggests that the diffraction
> data contained this information. Why Rietveld refinement can not be
> used for this purpose?
> I realize that most simple questions may be most difficult to answer,
> but nevertheless...
>
> Regards,
> Leonid
>
>
> __
> Do You Yahoo!?
> Tired of spam? Yahoo! Mail has the best spam protection around
> http://mail.yahoo.com
Size distribution from Rietveld refinement
Hi All. Regarding the RR ceria. The analysis carried out by us and discussed in Armstrong et al (2004a,b) did not assume a lognormal distribution, but tested the distribution model. The results from the Bayesian/MaxEnt methods, were free of any distribution function. Additional analysis showed that a lognormal distribution function fitted the Bayesian/MaxEnt results reasonable well. Regards, Nicholas - Original Message - From: Leonid Solovyov <[EMAIL PROTECTED]> Date: Monday, November 22, 2004 9:12 pm > Dear Rietvelders, > > Despite the heated discussion of the problem, the initial question, > which, actually, concerned the size distribution from Rietveld > refinement, seems to be unsettled. > Can we derive ANY information on the crystallite size distribution > (based on sensible assumptions) from the Thompson-Cox-Hastings > size-broadening parameters P and X normally obtained from Rietveld > refinement? > For the Ceria Size-Strain Round Robin sample the crystallite > distribution dispersion was determined from the profile analysis > assuming lognormal distribution. This suggests that the diffraction > data contained this information. Why Rietveld refinement can not be > used for this purpose? > I realize that most simple questions may be most difficult to answer, > but nevertheless... > > Regards, > Leonid > > > __ > Do You Yahoo!? > Tired of spam? Yahoo! Mail has the best spam protection around > http://mail.yahoo.com > -- UTS CRICOS Provider Code: 00099F DISCLAIMER: This email message and any accompanying attachments may contain confidential information. If you are not the intended recipient, do not read, use, disseminate, distribute or copy this message or attachments. If you have received this message in error, please notify the sender immediately and delete this message. Any views expressed in this message are those of the individual sender, except where the sender expressly, and with authority, states them to be the views the University of Technology Sydney. Before opening any attachments, please check them for viruses and defects.
Re: rietveld refinement
>Going back to Leonid's question, well the answer is easy: check the >premises... the assumptions behind the use of the TCH function are >not >compatible with he presence of a lognormal distribution of domains. But the TCH function gave ALMOST PERFECT fit for the Size-Strain Round Robin profiles. Where do we loose information applying THC in Rietveld refinement? In this "ALMOST"? Or, maybe, the distribution dispersion was erroneously determined in the SSRR and, actually, this information can not be unambiguously derived solely from diffraction? Leonid __ Do you Yahoo!? Meet the all-new My Yahoo! - Try it today! http://my.yahoo.com
Re: rietveld refinement
just my 2 cents... > Could I be so stupid to say that such kind of works, including mine, are > nothing? following Nicolae, I should also add to the list myself as well as most people participating to the four editions of the size-strain conference/meeting/workshop and all participants to Davor's size-strain round-robin. I bet people should spend more time in the library... this is the point. This is also a self criticism as I'm not the best library addict (though, online resources has simplified life enormously)... We should not try to use line profile analysis methods as a black box: it is easy to obtain numbers from measured data (with a proper software a computer can do it automatically), but then it is in the ability of the scientist to attach them a proper physical meaning. What it is difficult (perhaps impossible?) is willing and pretending to do it in the general case as we're dealing with something that has no precise rules (domain size, shape and their distributions are not properties of the materials, nor they can be easily predicted in advance). Some simple cases have been studied and some references already posted by several people in here, and in most of them the agreement between diffraction and alternative techniques is quite good: just in few cases, though, enough information is available to interpret the strain broadening fully in terms of physical defects present in the material, or to model the size term using a more or less complex distribution of (iso-shape) domains. But also in those cases the result is the one compatible with the model assumptions and does not pretend to be "God's truth". So welcome the round robin on a more complex sample to test the maturity of the algorithms (they should be even tested on simpler examples, as concluded on the latest size-strain conference, but that's another story..), but beware that without any a priori info (or with a wrong one!), a vast set of odd results can be obtained. As a comparison, it would be like pretending to do a search match, a structure solution or, even worse, a Rietveld refinement on a material for which we don't know any chemical information... Going back to Leonid's question, well the answer is easy: check the premises... the assumptions behind the use of the TCH function are not compatible with he presence of a lognormal distribution of domains. It can be proven mathematically that the Fourier coefficients for a profile describing a lognormal distribution of domains have a hook at low Fourier number, hook that cannot be reproduced by any whatsoever voigtian or voigtian-like curve. This is a common problem in the use of Voigt and voigt-like curves in describing the peak profiles from nanocrystalline powders and is also the main source of the "superlorentzian" peak tails (they are a trick to get rid of the physical information contained in the profile ;) we are a bit masochist, aren't we?) Best regards Mat -- Matteo Leoni Department of Materials Engineering and Industrial Technologies University of Trento 38050 Mesiano (TN) ITALY Tel +39 0461 882416e-mail: [EMAIL PROTECTED] Fax +39 0461 881977Web: www.matteoleoni.ing.unitn.it
Size distribution from Rietveld refinement
Dear Rietvelders, Despite the heated discussion of the problem, the initial question, which, actually, concerned the size distribution from Rietveld refinement, seems to be unsettled. Can we derive ANY information on the crystallite size distribution (based on sensible assumptions) from the Thompson-Cox-Hastings size-broadening parameters P and X normally obtained from Rietveld refinement? For the Ceria Size-Strain Round Robin sample the crystallite distribution dispersion was determined from the profile analysis assuming lognormal distribution. This suggests that the diffraction data contained this information. Why Rietveld refinement can not be used for this purpose? I realize that most simple questions may be most difficult to answer, but nevertheless... Regards, Leonid __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
Re: rietveld refinement
Hi, At the moment there is development of a NIST Nanocrystallite Size Standard Reference Material (SRM1979). Jim Cline and I are working on this SRM. It will include two materials: (1) CeO2 with spherical crystallite shape and size distribution in the ~20nm size range (isotropic shape); (2) ZnO with cylindrical or hexagonal prismatic crystallite shape with height in the, H~60-80nm and diameter, D~20-30nm range (anisotropic shape). This outlined in introduction of Armstrong et al (2004b) chapt.8, in "Diffraction analysis of the microstructure of materials", Springer-Verlag, pp.187--227. In both cases the Bayesian/MaxEnt method will be used to determine the *physical* size distribution and shape. For example in the case of (1), the method tests the model for a spherical crystallite shape, while also testing various size distribution models i.e lognormal, gamma etc. For this case a lognormal size distribution has found to be the appropriate distribution. In the case of (2) the distributions are for H and D, respectively, while testing different shape models can also be carried out. This presently being developed. The Bayesian/MaxEnt method is a general formulation which tests the underlying assumption of various models and determines the most probable size distribution and crystallite shape. There is lots of working/development going on!! Regards, Nicholas - Original Message - From: Nicolae Popa <[EMAIL PROTECTED]> Date: Monday, November 22, 2004 7:12 pm > > > > > It is also true that no development has been done for anisotropy. > Not yet! > > > > Well, if all previous works about trying to take account of > size/strain> anisotropy in the Rietveld method are nothing yet, > this allows to > > close the discussion. Let us wait for really serious developments to > > come. > > You not correctly understood me (I would like to believe that not > ill-disposed). > I said that no development for size anisotropy has been done including > "physical" size distributions (like lognormal, etc.) as were done > for the > isotropic case. > For example: Langford, Louer & Scardi, JAC (2000) 33, 964-974 and > Popa & > Balzar JAC (2002) 35, 338-346. > Concerning previous (phenomenological) works trying to take account of > strain/size anisotropy in the Rietveld method, I have myself a > contribution:"The (hkl) dependence of diffraction-line broadening > caused by strain and > size for all Laue groups in Rietveld refinement, N. C. Popa, J. > Appl. Cryst. > (1998) 31, 176-180." > Could I be so stupid to say that such kind of works, including > mine, are > nothing? > > Best wishes, > Nicolae Popa > > > > > > -- UTS CRICOS Provider Code: 00099F DISCLAIMER: This email message and any accompanying attachments may contain confidential information. If you are not the intended recipient, do not read, use, disseminate, distribute or copy this message or attachments. If you have received this message in error, please notify the sender immediately and delete this message. Any views expressed in this message are those of the individual sender, except where the sender expressly, and with authority, states them to be the views the University of Technology Sydney. Before opening any attachments, please check them for viruses and defects.
Re: rietveld refinement
At least the anisotropic formalism by Popa (J. Appl. Cryst. (1998) 31, 176-180) has been used for anisotropic shape refinements using the MAUD Rietveld codes, on textured samples: Thin Solid Films 450, 2004, 216-221. daniel A 11:12 AM 11/22/04 +0300, vous avez écrit : > > It is also true that no development has been done for anisotropy. Not yet! > > Well, if all previous works about trying to take account of size/strain > anisotropy in the Rietveld method are nothing yet, this allows to > close the discussion. Let us wait for really serious developments to > come. You not correctly understood me (I would like to believe that not ill-disposed). I said that no development for size anisotropy has been done including "physical" size distributions (like lognormal, etc.) as were done for the isotropic case. For example: Langford, Louer & Scardi, JAC (2000) 33, 964-974 and Popa & Balzar JAC (2002) 35, 338-346. Concerning previous (phenomenological) works trying to take account of strain/size anisotropy in the Rietveld method, I have myself a contribution: "The (hkl) dependence of diffraction-line broadening caused by strain and size for all Laue groups in Rietveld refinement, N. C. Popa, J. Appl. Cryst. (1998) 31, 176-180." Could I be so stupid to say that such kind of works, including mine, are nothing? Best wishes, Nicolae Popa A Quantitative Texture Analysis Internet Course: http://qta.ecole.ensicaen.fr/ The Crystallographic Open Database: http://www.crystallography.net Daniel Chateigner Professeur Co-Editor Journal of Applied Crystallography CRISMAT-ENSICAEN, UMR CNRS n° 6508 Bd. Maréchal Juin, 14050 Caen FRANCE Tel prof: 33 (0) 231452611 Fax: 33 (0) 231951600 http://www.ecole.ensicaen.fr/~chateign/danielc/
Re: rietveld refinement
> > It is also true that no development has been done for anisotropy. Not yet! > > Well, if all previous works about trying to take account of size/strain > anisotropy in the Rietveld method are nothing yet, this allows to > close the discussion. Let us wait for really serious developments to > come. You not correctly understood me (I would like to believe that not ill-disposed). I said that no development for size anisotropy has been done including "physical" size distributions (like lognormal, etc.) as were done for the isotropic case. For example: Langford, Louer & Scardi, JAC (2000) 33, 964-974 and Popa & Balzar JAC (2002) 35, 338-346. Concerning previous (phenomenological) works trying to take account of strain/size anisotropy in the Rietveld method, I have myself a contribution: "The (hkl) dependence of diffraction-line broadening caused by strain and size for all Laue groups in Rietveld refinement, N. C. Popa, J. Appl. Cryst. (1998) 31, 176-180." Could I be so stupid to say that such kind of works, including mine, are nothing? Best wishes, Nicolae Popa
Re: rietveld refinement
Hi, With regards to size/shape/distribution analysis of line profiles, the papers by Armstrong et al. (2004a,b,c) discusses a Bayesian/Maximum Entropy method, that determines these quantities from the line profile data. This can also resolve bimodal distributions from line profile data. This method tests models for shape/size distribution and modal properties using Bayesian analysis. The maximum entropy components is a generalisation of the approach presented in A. Le Bail and D. Lou?r. J. Appl. Cryst. (1978). 11, 50-55. It preserves the positivity of the distribution, determines the most probable distribution give the line profile data, instrument profile and statistical noise. Recent publications can be found at the following: http://nvl.nist.gov/pub/nistpubs/jres/109/1/cnt109-1.htm; Armstrong et al (2004b) chapt.8, in "Diffraction analysis of the microstructure of materials", Springer-Verlag, pp.187--227; WA5 Armstrong et al. (2004c), http://www.aip.org.au/wagga2004/. Regards,Nicholas Dr Nicholas Armstrong Department of Applied Physics University of Technology Sydney PO Box 123 Broadway NSW 2007 Ph: (+61-2) 9514-2203 Fax: (+61-2) 9514-2219 E-mail: [EMAIL PROTECTED] - Original Message - From: Armel Le Bail <[EMAIL PROTECTED]> Date: Sunday, November 21, 2004 11:10 pm > > It is also true that no development has been done for anisotropy. > Not yet! > > Well, if all previous works about trying to take account of > size/strainanisotropy in the Rietveld method are nothing yet, this > allows to > close the discussion. Let us wait for really serious developments to > come. > > Armel > > > > -- UTS CRICOS Provider Code: 00099F DISCLAIMER: This email message and any accompanying attachments may contain confidential information. If you are not the intended recipient, do not read, use, disseminate, distribute or copy this message or attachments. If you have received this message in error, please notify the sender immediately and delete this message. Any views expressed in this message are those of the individual sender, except where the sender expressly, and with authority, states them to be the views the University of Technology Sydney. Before opening any attachments, please check them for viruses and defects.
Re: rietveld refinement
Title: RE: rietveld refinement I'm afraid that you got the wrong end of the stick -I wasn't talking about the application of peak broadening to size distribution, I was commenting that determining crystallite shape is perfectly possible (some comments were flying that said otherwise), and I've done it myself. For that purpose a sample approaching monodisperse is helpful. It would be a bit pointless trying to determine the size distribution of a monodisperse sample !! :-) I did send an email that I think only went to Armel by mistake making this clearer. I was having a slow morning! :-) Pam -Original Message- From: Nicolae Popa To: [EMAIL PROTECTED] Sent: 11/21/2004 5:04 AM Subject: Re: rietveld refinement Doesn't help with a size distribution, as it only works well for a relatively monodisperse material - but it does work under some circumstances. Pam I disagree, it works also for large dispersion. One example you can find in JAC (2002) 35, 338-346, "Sample 2". It is true that the specific peak profile (that can be "superlorentzian") can not be found in no available Rietveld code. It is also true that no development has been done for anisotropy. Not yet! Best wishes, Nicolae Popa
Re: rietveld refinement
It is also true that no development has been done for anisotropy. Not yet! Well, if all previous works about trying to take account of size/strain anisotropy in the Rietveld method are nothing yet, this allows to close the discussion. Let us wait for really serious developments to come. Armel
Re: rietveld refinement
Title: RE: rietveld refinement Doesn't help with a size distribution, as it only works well for a relatively monodisperse material - but it does work under some circumstances. Pam I disagree, it works also for large dispersion. One example you can find in JAC (2002) 35, 338-346, "Sample 2". It is true that the specific peak profile (that can be "superlorentzian") can not be found in no available Rietveld code. It is also true that no development has been done for anisotropy. Not yet! Best wishes, Nicolae Popa
Re: rietveld refinement
> So I cannot let say that "Significantly different "physical" > size distributions could describe equally well the peak profile". > This is confusing. You may say that : significantly different > crystallite shapes could describe equally well the peak profile > in cubic symmetry. I am not sure that this sentence is > valuable equally for other symmetries when looking at all Sorry, it seems me that rather your sentence is confusing, not mine. In the example with CeO2 the crystallites are quite spherical (one shape) even seen by microscope. But two significantly different distributions of the sphere radius (6a1, 6a2) (lognormal & gamma, respectively) given quite the same column length distribution (6b1, 6b2) and practically the same peak profile. It is no matter here of different crystallite shapes because the shape is unique (sphere). And also the cubic symmetry has no relevance, this should happen for any symmetry (I mean not an unique solution for the sphere radius distribution). (By the way, the sample of CeO2 in discussion is just the sample used in the round-robin paper that you co-authored; in this last paper we used only the lognormal distribution, but doesn't mean that this is the unique solution from powder diffraction). Concerning the different crystallite shapes, this is another storry. I said that even if the cristallites are not spherical, it is not obligatory to observe an anisotropic size broadening effect. Not spherical crystallites is only the necessary condition for size anisotropy effect, but not sufficient. The anisotropic size broadening effect is observable only if the non spherical shape is preferentially orientated with respect to the crystal axes (don't confuse with the texture). It is the case of your nickel hydroxyde in which the plate-like normal is preferentially oriented along the hexagonal c axis. But, if the not spherical crystallite shapes are randomly oriented with respect to the crystal axes (which is possible) the size broadening effect is isotropic and, only from powder diffraction, we can conclude erroneously that the crystallites are spherical. On the other hand, if the anisotropy is observed, the crystallite shape (and the distributions of specific radii) can not be uniquely determined only from powder diffraction. What we can determine is an apparent shape (and column lengths averages). Has any sense, in this case, to search for so called "physical models", or we have to be content with "phenomenological" findings (so much blamed, at least implicitely)? It is only a question, valid also for the strain effect. > So, let us have more fun with a size strain round robin on some > complex sample (or even a size-only round robin not on a > cubic compound ;-). I agree entirely. Best wishes, Nicolae Popa
Re: rietveld refinement
can anyone send me a soft copy of the following paper J. Appl. Cryst. (1978). 11, 50-55. thanks venkat +++ M Venkata Kamalakar Junior Research Fellow, S.N.Bose.National Centre for Basic Sciences, Block-JD, Sector-3, Salt Lake, Kolkata, Pin: 700 098. Phone no: 033 23355705/6/7/8 Extn: 404, 104, 301. +++ -- Original Message --- From: Armel Le Bail <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] Sent: Fri, 19 Nov 2004 08:43:11 +0100 > >It is a separate question to what extent those distributions are > >"physical"... > > Simple attempts to establish that at least the size distributions > obtained from a mixture of two samples with same composition > and two very different size distributions, are close to the > expected result, establishing some self-consistency of the > methodology, if not that they are "physical" (I believe they are > "physical" in case of size-only effect). > > See for instance J. Appl. Cryst. (1978). 11, 50-55. > This can be found also (in french) in a thesis : > http://tel.ccsd.cnrs.fr/documents/archives0/00/00/70/41/index_fr.html > (self citation...;-). Things have not changed a lot since these > old times. > > Armel --- End of Original Message ---
RE: rietveld refinement
can you please send me the soft copy of the paper you referred to. We don't have access to that journal... very much sincerely yours venkat From: Armel Le Bail <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] Sent: Fri, 19 Nov 2004 16:49:42 +0100 > >I'd have to disagree on this point - troublemaker I suppose! I've > >followed the work by Langford and Louer closely, and have successfully > >applied their techniques > > I do not understand on what point exactly you disagree. > The cited paper about size effect in nickel hydroxyde > is co-authored by D. Louer, and may still seem kosher to him ;-). > The full reference is : > > A. Le Bail and D. Louër. J. Appl. Cryst. (1978). 11, 50-55 > [doi:10.1107/S0021889878012662] > Title: Smoothing and validity of crystallite-size distributions from > X-ray line-profile analysis Abstract: A smoothing procedure is > described which eliminates spurious details on crystallite-size > distribution functions deduced from X-ray line profiles. It is based > on a least-squares process with a stabilization scheme and is > applied to composite specimens prepared by mixing known quantities > of samples of nickel hydroxide, whose crystallite size-distribution > functions were previously determined. Calculated and observed > distributions and average sizes are compared. The results are > reasonably good and show the self-consistency of the method. > > Best regards, > > Armel --- End of Original Message ---
Re: rietveld refinement
Let me put a more particular question on the size estimation from Rietveld refinement. If we refined the size-broadening parameters P and X of the Thompson-Cox-Hastings function (as they are defined in J. Appl. Cryst. (2004) 911) and corrected them for the instrumental contribution, then can we say something about the coherent domain size DISTRIBUTION assuming the domains approximately spherical? Leonid Solovyov __ Do you Yahoo!? Meet the all-new My Yahoo! - Try it today! http://my.yahoo.com
