Re: quantitative analysis - perovskites - preferred orientation
Dear Lukasz, First of all, in the majority of Rietveld programs the uniaxial preferred orientation (such as [100]) can not be handled adequately for cubic systems since the programs normally generate only one symmetrically equivalent hkl for a diffraction peak. In DDM, for such cases, I included a special option (Expanded hkl) to generate all equivalent hkl's for every peak. This option makes the refinement process slower and also may require some manual settings for initial parameter values. Another alternative for cubic systems is spherical harmonics. As for the estimated error of the refined PO component, it's really wise to check if it exceeds the refined value, but it should be done at the final stage only, as at initial stages all errors may be high due to the incompleteness of refinement. Best regards, Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660036, Akademgorodok 50/24, Krasnoyarsk, Russia http://sites.google.com/site/solovyovleonid *** On Thursday, February 6, 2014 5:37 PM, Łukasz Kruszewski lkruszew...@twarda.pan.pl wrote: Dear Madam/Sir(s), I am performing Rietveld analysis for a sample containing perovskites (CaTiO3 and SrTiO3). When putting-in a preferred orientation (PO) correction (100 direction, as the crystals are cubic-like), I obtain better Rwp and GOF i.e. chi-squared values (9.63 and 1.5, respectively) than in the case of not using this correction (Rwp = 10.62 and GOF = 1.65). However, the values of the PO corrections are higher than the errors calculated. All the other parameters including the graphical fit, background etc., seem to be unchanged. I am also convinced about the correctness of any input, with my diffractometer calibrated with LaB6 and Si standards, and Beq / Uiso parameters taken directly from the CIF files provided, so that the microabsorption factor may likely be rejected (?). My guess is that putting in the preferred orientation might artificially, somehow, make the fit better, maybe due to some interdependence? Could you please kindly suggests if obtaining better statistics (Rwp, GOF) by getting a correction values below the corresponding errors could be treated as a good result? Best regards! -- Łukasz Kruszewski, Ph.D., adjunct Polish Academy of Sciences Institute of Geological Sciences X-Ray Diffraction Laboratory (coordinator) Twarda 51/55 str. 00-818 Warsaw Poland ++ Please do NOT attach files to the whole list alan.he...@neutronoptics.com Send commands to 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/ Please do NOT attach files to the whole list alan.he...@neutronoptics.com Send commands to 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/ ++
Re: Quantitative analysis
[EMAIL PROTECTED] a écrit : Hi Blaise In Bragg-Brentano mode, sample spinning does nothin for PO. This is because the diffraction vector is normal to the sample surface, and sample spinning rotates along this vector. That's wrong! As I have already written, the empirical PO corrections like March-Dollase and Rietveld-Toraya suppose that the PO is fibre-like (axial symmetry). If your sample does not have fibre-like PO, you can create it by sample spinning. Radovan Spinning does increase your particle statistics, which almost always helps. If you're looking at a capillary, spinning the capillary does help with PO, but just being in a capillary helps PO. As to spinning speeds, a good guide is one revolution per data point. Cheers Matthew Matthew Rowles CSIRO Minerals Box 312 Clayton South, Victoria AUSTRALIA 3169 Ph: +61 3 9545 8892 Fax: +61 3 9562 8919 (site) Email: [EMAIL PROTECTED] -- Radovan Cerny Laboratoire de Cristallographie 24, quai Ernest-Ansermet CH-1211 Geneva 4, Switzerland Phone : [+[41] 22] 37 964 50, FAX : [+[41] 22] 37 961 08 mailto : [EMAIL PROTECTED] URL: http://www.unige.ch/sciences/crystal/cerny/rcerny.htm
RE: Quantitative analysis
hi all, not only fibre like, but single component fibre, and with the fibre axis parrallel to the sample normal (i.e. cyclic fibre. this is very restrictive and generally does not correspond to the real texture. Contrarilly to what has been said here or there, the March-Dollase does not ensure PO normalisation, but only the normalisation of this single component, there is then no physical restriction between all hkl lines in terms of crystal angles, which gives rise to a lot of fitting space with unreasonable solutions either in terms of QTA or QPA. A physically based correction for PO needs the calculation of the ODF, and more than a single pattern to be measured. But this is the price to pay for a corect estimate of phase amounts in textured samples. daniel -- Daniel Chateigner Professeur CRISMAT-ENSICAEN Bd. M. Juin 14050 Caen, France http://www.ecole.ensicaen.fr/~chateign/danielc/
Re: Quantitative analysis
Dear Mario, One more possible problem of applying preferred orientation corrections in QPA is that not all of them are normalized. For example, the March-Dollase correction is normalized and can be applied safely, but the Rietveld-Toraya correction is inapplicable to QPA as it does not preserve the scale normalization. Best regards, Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology K. Marx av., 42 660049, Krasnoyarsk Russia Phone: +7 3912 495663 Fax: +7 3912 238658 www.icct.ru/eng/content/persons/Sol_LA *** --- On Mon, 10/27/08, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote: From: [EMAIL PROTECTED] [EMAIL PROTECTED] Subject: Quantitative analysis To: Rietveld_l@ill.fr Date: Monday, October 27, 2008, 3:48 PM Dear all, I have this question, I have been refined one mixture (of well-know percentage composition) of CaCO3, CaF2, SiO2 and Al2O3, with preferential orientation in CaCO3 (104) and CaF2 (111) with good results. When I add to the mixture FeCO3 and I refine with preferential orientation (104), it happens that when I don´t apply the preferential orientation in all this phases, I have correct values of percentage composition, but when I apply the preferential orientation the refinement is good but with incorrect values of percentage composition. This experiment has been taken in Bragg Brentano geometry. How I should refine this mixture? Thanks a lot by your help. Mario Macías Universidad Industrial de Santander Colombia
RE: Quantitative analysis
Sorry to disagree. Experience tells me otherwise - the March-Dollase correction has nearly always led to poor quant results for me. It most certainly cannot be applied safely. Martin -- M Vickers Dept of Chemistry UCL Subject: Re: Quantitative analysis Date: Tue, 28 Oct 2008 02:53:20 -0700 From: [EMAIL PROTECTED] To: Rietveld_l@ill.fr Dear Mario, One more possible problem of applying preferred orientation corrections in QPA is that not all of them are normalized. For example, the March-Dollase correction is normalized and can be applied safely, but the Rietveld-Toraya correction is inapplicable to QPA as it does not preserve the scale normalization. Best regards, Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology K. Marx av., 42 660049, Krasnoyarsk Russia Phone: +7 3912 495663 Fax: +7 3912 238658 www.icct.ru/eng/content/persons/Sol_LA _ See the most popular videos on the web http://clk.atdmt.com/GBL/go/115454061/direct/01/
Re: Quantitative analysis
Martin, The reason of your bad experience with March-Dollase can be different, however, Leonid was right. The March-Dollase is normalized, the Rietveld-Toraya not. It can be easily normalized (see for example J. Appl. Cryst. 28(1995)247-253) but in all Rietveld codes I know it is not. Best radovan Martin a écrit : Sorry to disagree. Experience tells me otherwise - the March-Dollase correction has nearly always led to poor quant results for me. It most certainly cannot be applied safely. Martin -- M Vickers Dept of Chemistry UCL Subject: Re: Quantitative analysis Date: Tue, 28 Oct 2008 02:53:20 -0700 From: [EMAIL PROTECTED] To: Rietveld_l@ill.fr Dear Mario, One more possible problem of applying preferred orientation corrections in QPA is that not all of them are normalized. For example, the March-Dollase correction is normalized and can be applied safely, but the Rietveld-Toraya correction is inapplicable to QPA as it does not preserve the scale normalization. Best regards, Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology K. Marx av., 42 660049, Krasnoyarsk Russia Phone: +7 3912 495663 Fax: +7 3912 238658 www.icct.ru/eng/content/persons/Sol_LA For the best free wallpapers from MSN Click here! http://wallpapers.msn.com/?ocid=[B001MSN42A0716B] -- Radovan Cerny Laboratoire de Cristallographie 24, quai Ernest-Ansermet CH-1211 Geneva 4, Switzerland Phone : [+[41] 22] 37 964 50, FAX : [+[41] 22] 37 961 08 mailto : [EMAIL PROTECTED] URL: http://www.unige.ch/sciences/crystal/cerny/rcerny.htm
RE: Quantitative analysis
Mario, You may want to check for the presence of solid solution in your siderite (especially Ca and Mg). In my experience refining the PO in siderite with measurable amounts of Ca or Mg correlates significantly with the occupancy if the Fe/(Ca or Mg) ratio is not constrained to the true chemistry. The chemistry may be estimated by the d104 shift. Dipo Omotoso Natural Resources Canada CETC-Devon #1 Oil Patch drive, Devon AB. T9G 1A8. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Mon 10/27/2008 7:10 PM To: [EMAIL PROTECTED]; Rietveld_l@ill.fr Subject: RE: Quantitative analysis Dear Mario, Please tell me a little about the data collection conditions you used for this work:- How was the sample prepared (hand ground, micronised in McCrone mill ) What was the tube target Cu, Co, other ?? Cheers Ian Madsen From: [EMAIL PROTECTED] [EMAIL PROTECTED] Sent: Tuesday, October 28, 2008 2:48 AM To: Rietveld_l@ill.fr Subject: Quantitative analysis Dear all, I have this question, I have been refined one mixture (of well-know percentage composition) of CaCO3, CaF2, SiO2 and Al2O3, with preferential orientation in CaCO3 (104) and CaF2 (111) with good results. When I add to the mixture FeCO3 and I refine with preferential orientation (104), it happens that when I don´t apply the preferential orientation in all this phases, I have correct values of percentage composition, but when I apply the preferential orientation the refinement is good but with incorrect values of percentage composition. This experiment has been taken in Bragg Brentano geometry. How I should refine this mixture? Thanks a lot by your help. Mario Macías Universidad Industrial de Santander Colombia
RE: Quantitative analysis
While my coffee pot gurgles away here's my tuppence worth As mentioned by previous answers prevention is MUCH better than cure. Having said that a couple of comments. If there's significant PO then it's a pretty sure thing that the particles are not spherical - so you can forget the Brindley correction which assumes spherical (and also monodisperse BTW) particles. PO is also strongly suggestive (but not certain) of fairly large particles, so microabsorption could be pretty severe. In this case with FeCO3 and Cu radiation microabsorption is going to be an issue independent of whether the PO correction preserves the scale normalization. Pam Dr Pamela Whitfield MRSC CChem Energy Materials Institute for Chemical Process and Environmental Technology (ICPET) Building M12 National Research Council Canada 1200 Montreal Road Ottawa ON K1A 0R6 CANADA Tel: (613) 998-8462Fax: (613) 991 2384 Email: [EMAIL PROTECTED] -Original Message- From: Leonid Solovyov [mailto:[EMAIL PROTECTED] Sent: October 28, 2008 5:53 AM To: Rietveld_l@ill.fr Subject: Re: Quantitative analysis Dear Mario, One more possible problem of applying preferred orientation corrections in QPA is that not all of them are normalized. For example, the March-Dollase correction is normalized and can be applied safely, but the Rietveld-Toraya correction is inapplicable to QPA as it does not preserve the scale normalization. Best regards, Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology K. Marx av., 42 660049, Krasnoyarsk Russia Phone: +7 3912 495663 Fax: +7 3912 238658 www.icct.ru/eng/content/persons/Sol_LA *** --- On Mon, 10/27/08, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote: From: [EMAIL PROTECTED] [EMAIL PROTECTED] Subject: Quantitative analysis To: Rietveld_l@ill.fr Date: Monday, October 27, 2008, 3:48 PM Dear all, I have this question, I have been refined one mixture (of well-know percentage composition) of CaCO3, CaF2, SiO2 and Al2O3, with preferential orientation in CaCO3 (104) and CaF2 (111) with good results. When I add to the mixture FeCO3 and I refine with preferential orientation (104), it happens that when I don´t apply the preferential orientation in all this phases, I have correct values of percentage composition, but when I apply the preferential orientation the refinement is good but with incorrect values of percentage composition. This experiment has been taken in Bragg Brentano geometry. How I should refine this mixture? Thanks a lot by your help. Mario Macías Universidad Industrial de Santander Colombia
RE: Quantitative analysis
I agree that it's always best to avoid preferred orientation, but that is easier said than done on a routine basis. I have personally had good luck with the M-D PO correction on many known samples, as long as the PO was not severe. However, I imagine that Mario's problems are related to microabsorption in this case. Mario, if you can re-measure your data with a Co or Fe tube, it would be a good test of this. Dave Bish At 08:51 AM 10/28/2008 -0400, Martin wrote: Sorry to disagree. Experience tells me otherwise - the March-Dollase correction has nearly always led to poor quant results for me. It most certainly cannot be applied safely. Martin -- M Vickers Dept of Chemistry UCL -- Subject: Re: Quantitative analysis Date: Tue, 28 Oct 2008 02:53:20 -0700 From: [EMAIL PROTECTED] To: Rietveld_l@ill.fr Dear Mario, One more possible problem of applying preferred orientation corrections in QPA is that not all of them are normalized. For example, the March-Dollase correction is normalized and can be applied safely, but the Rietveld-Toraya correction is inapplicable to QPA as it does not preserve the scale normalization. Best regards, Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology K. Marx av., 42 660049, Krasnoyarsk Russia Phone: +7 3912 495663 Fax: +7 3912 238658 www.icct.ru/eng/content/persons/Sol_LA -- For the best free wallpapers from MSN Click here!
RE: Quantitative analysis
Dear all, the well-known data are: CaCO3 (20%), CaF2 (35%), SiO2 (1%), Al2O3 (20%), and FeCO3 (24%). The data obtained without PO are: CaCO3 (24%), CaF2 (36%), SiO2 (1%), Al2O3 (17%), and FeCO3 (23%). The data obtained with PO are: CaCO3 (19%), CaF2 (32%), SiO2 (2%), Al2O3 (31%), and FeCO3 (16%). it seems to have a problem among Al2O3 and FeCO3 data after PO. Mario. Dear all, The data collection conditions is: hand grind (35 microns), scan: 2Theta/Theta Coupled, to steps 2 sec., target Cu, graphite monochromator, side loading. The correction of preferential orientation has been refined by March-Dollase model. Thanks a lot, Mario. Dear Mario, Please tell me a little about the data collection conditions you used for this work:- How was the sample prepared (hand ground, micronised in McCrone mill ) What was the tube target Cu, Co, other ?? Cheers Ian Madsen From: [EMAIL PROTECTED] [EMAIL PROTECTED] Sent: Tuesday, October 28, 2008 2:48 AM To: Rietveld_l@ill.fr Subject: Quantitative analysis Dear all, I have this question, I have been refined one mixture (of well-know percentage composition) of CaCO3, CaF2, SiO2 and Al2O3, with preferential orientation in CaCO3 (104) and CaF2 (111) with good results. When I add to the mixture FeCO3 and I refine with preferential orientation (104), it happens that when I don´t apply the preferential orientation in all this phases, I have correct values of percentage composition, but when I apply the preferential orientation the refinement is good but with incorrect values of percentage composition. This experiment has been taken in Bragg Brentano geometry. How I should refine this mixture? Thanks a lot by your help. Mario Macías Universidad Industrial de Santander Colombia
RE: Quantitative analysis
I am learning QPA and am worried about PO. I wonder why sample spinning isn't discussed more. I am luckily able to barrow time on a newer diffractometer with a sample spinner. Does this reduce PO? Or completely eliminate it? There is a set up variable in GSAS for whether you are spinning the sample - are there guidelines for how many revolutions to spin the sample if you just want to reduce PO? Thanks to all for there help!!! Blaise * * * * * * * * * * * * * Blaise Mibeck Research Scientist Energy Environmental Research Center University of North Dakota 15 North 23rd Street, Stop 9018 Grand Forks, ND 58202-9018 Phone: (701) 777-5077 Email: [EMAIL PROTECTED] -Original Message- From: David L. Bish [mailto:[EMAIL PROTECTED] Sent: Tuesday, October 28, 2008 9:09 AM To: Martin; [EMAIL PROTECTED]; rietveld_l@ill.fr Subject: RE: Quantitative analysis I agree that it's always best to avoid preferred orientation, but that is easier said than done on a routine basis. I have personally had good luck with the M-D PO correction on many known samples, as long as the PO was not severe. However, I imagine that Mario's problems are related to microabsorption in this case. Mario, if you can re-measure your data with a Co or Fe tube, it would be a good test of this. Dave Bish At 08:51 AM 10/28/2008 -0400, Martin wrote: Sorry to disagree. Experience tells me otherwise - the March-Dollase correction has nearly always led to poor quant results for me. It most certainly cannot be applied safely. Martin -- M Vickers Dept of Chemistry UCL Subject: Re: Quantitative analysis Date: Tue, 28 Oct 2008 02:53:20 -0700 From: [EMAIL PROTECTED] To: Rietveld_l@ill.fr Dear Mario, One more possible problem of applying preferred orientation corrections in QPA is that not all of them are normalized. For example, the March-Dollase correction is normalized and can be applied safely, but the Rietveld-Toraya correction is inapplicable to QPA as it does not preserve the scale normalization. Best regards, Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology K. Marx av., 42 660049, Krasnoyarsk Russia Phone: +7 3912 495663 Fax: +7 3912 238658 www.icct.ru/eng/content/persons/Sol_LA For the best free wallpapers from MSN Click here! http://wallpapers.msn.com/?ocid
Re: Quantitative analysis
The empirical PO corrections like March-Dollase or Rietveld-Toraya can correct only for fibre like PO, i.e. symmetrical around one axis. If it is not your case, you can make it fibre like by spinning, if you spin around the PO vector. If not than see J. Appl. Cryst. 28(1995)247-253. However, there are few other limitations, which are usually completly ignored: The distribution of crystallites around any pole hkl must be axially symmetrical either, so-called disc- or rod-shape like behavior. No way to do it by spinning ... Most of implementations of these corrections in the Rietveld codes also assume another condition: The texture axis is parallel (or perpendicular) to the diffraction vector for all measured hkls. This condition is fullfilled only in Bragg-Brentano or Debye-Scherrer geometries. Surprising that it still works ... Radovan Mibeck, Blaise a écrit : I am learning QPA and am worried about PO. I wonder why sample spinning isn’t discussed more. I am luckily able to barrow time on a newer diffractometer with a sample spinner. Does this reduce PO? Or completely eliminate it? There is a set up variable in GSAS for whether you are spinning the sample – are there guidelines for how many revolutions to spin the sample if you just want to reduce PO? Thanks to all for there help!!! Blaise * * * * * * * * * * * * * Blaise Mibeck Research Scientist Energy Environmental Research Center University of North Dakota 15 North 23rd Street, Stop 9018 Grand Forks, ND 58202-9018 Phone: (701) 777-5077 Email: [EMAIL PROTECTED] mailto:[EMAIL PROTECTED] -Original Message- *From:* David L. Bish [mailto:[EMAIL PROTECTED] *Sent:* Tuesday, October 28, 2008 9:09 AM *To:* Martin; [EMAIL PROTECTED]; rietveld_l@ill.fr *Subject:* RE: Quantitative analysis I agree that it's always best to avoid preferred orientation, but that is easier said than done on a routine basis. I have personally had good luck with the M-D PO correction on many known samples, as long as the PO was not severe. However, I imagine that Mario's problems are related to microabsorption in this case. Mario, if you can re-measure your data with a Co or Fe tube, it would be a good test of this. Dave Bish At 08:51 AM 10/28/2008 -0400, Martin wrote: Sorry to disagree. Experience tells me otherwise - the March-Dollase correction has nearly always led to poor quant results for me. It most certainly cannot be applied safely. Martin -- M Vickers Dept of Chemistry UCL Subject: Re: Quantitative analysis Date: Tue, 28 Oct 2008 02:53:20 -0700 From: [EMAIL PROTECTED] To: Rietveld_l@ill.fr Dear Mario, One more possible problem of applying preferred orientation corrections in QPA is that not all of them are normalized. For example, the March-Dollase correction is normalized and can be applied safely, but the Rietveld-Toraya correction is inapplicable to QPA as it does not preserve the scale normalization. Best regards, Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology K. Marx av., 42 660049, Krasnoyarsk Russia Phone: +7 3912 495663 Fax: +7 3912 238658 www.icct.ru/eng/content/persons/Sol_LA http://www.icct.ru/eng/content/persons/Sol_LA For the best free wallpapers from MSN Click here! http://wallpapers.msn.com/?ocid -- Radovan Cerny Laboratoire de Cristallographie 24, quai Ernest-Ansermet CH-1211 Geneva 4, Switzerland Phone : [+[41] 22] 37 964 50, FAX : [+[41] 22] 37 961 08 mailto : [EMAIL PROTECTED] URL: http://www.unige.ch/sciences/crystal/cerny/rcerny.htm
RE: Quantitative analysis
Mario, From the information that you just gave, it appears that the corundum 012 and siderite 012 are not well resolved causing more of the siderite 012 intensity to be attributed to the corundum 012 and an overestimation of corundum. If it is a microabsorption problem, you wouldn't get a good QPA data without PO correction to start with. If you can, reduce the receiving slit size and run the sample again or don't correct for PO. Dipo Omotoso -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: October 28, 2008 8:24 AM To: Rietveld_l@ill.fr Subject: RE: Quantitative analysis Dear all, the well-known data are: CaCO3 (20%), CaF2 (35%), SiO2 (1%), Al2O3 (20%), and FeCO3 (24%). The data obtained without PO are: CaCO3 (24%), CaF2 (36%), SiO2 (1%), Al2O3 (17%), and FeCO3 (23%). The data obtained with PO are: CaCO3 (19%), CaF2 (32%), SiO2 (2%), Al2O3 (31%), and FeCO3 (16%). it seems to have a problem among Al2O3 and FeCO3 data after PO. Mario. Dear all, The data collection conditions is: hand grind (35 microns), scan: 2Theta/Theta Coupled, to steps 2 sec., target Cu, graphite monochromator, side loading. The correction of preferential orientation has been refined by March-Dollase model. Thanks a lot, Mario. Dear Mario, Please tell me a little about the data collection conditions you used for this work:- How was the sample prepared (hand ground, micronised in McCrone mill ) What was the tube target Cu, Co, other ?? Cheers Ian Madsen From: [EMAIL PROTECTED] [EMAIL PROTECTED] Sent: Tuesday, October 28, 2008 2:48 AM To: Rietveld_l@ill.fr Subject: Quantitative analysis Dear all, I have this question, I have been refined one mixture (of well-know percentage composition) of CaCO3, CaF2, SiO2 and Al2O3, with preferential orientation in CaCO3 (104) and CaF2 (111) with good results. When I add to the mixture FeCO3 and I refine with preferential orientation (104), it happens that when I don´t apply the preferential orientation in all this phases, I have correct values of percentage composition, but when I apply the preferential orientation the refinement is good but with incorrect values of percentage composition. This experiment has been taken in Bragg Brentano geometry. How I should refine this mixture? Thanks a lot by your help. Mario Macías Universidad Industrial de Santander Colombia
RE: Quantitative analysis
Thank you to all for your generous help... has been very important your information.. Mario. Mario, From the information that you just gave, it appears that the corundum 012 and siderite 012 are not well resolved causing more of the siderite 012 intensity to be attributed to the corundum 012 and an overestimation of corundum. If it is a microabsorption problem, you wouldn't get a good QPA data without PO correction to start with. If you can, reduce the receiving slit size and run the sample again or don't correct for PO. Dipo Omotoso -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: October 28, 2008 8:24 AM To: Rietveld_l@ill.fr Subject: RE: Quantitative analysis Dear all, the well-known data are: CaCO3 (20%), CaF2 (35%), SiO2 (1%), Al2O3 (20%), and FeCO3 (24%). The data obtained without PO are: CaCO3 (24%), CaF2 (36%), SiO2 (1%), Al2O3 (17%), and FeCO3 (23%). The data obtained with PO are: CaCO3 (19%), CaF2 (32%), SiO2 (2%), Al2O3 (31%), and FeCO3 (16%). it seems to have a problem among Al2O3 and FeCO3 data after PO. Mario. Dear all, The data collection conditions is: hand grind (35 microns), scan: 2Theta/Theta Coupled, to steps 2 sec., target Cu, graphite monochromator, side loading. The correction of preferential orientation has been refined by March-Dollase model. Thanks a lot, Mario. Dear Mario, Please tell me a little about the data collection conditions you used for this work:- How was the sample prepared (hand ground, micronised in McCrone mill ) What was the tube target Cu, Co, other ?? Cheers Ian Madsen From: [EMAIL PROTECTED] [EMAIL PROTECTED] Sent: Tuesday, October 28, 2008 2:48 AM To: Rietveld_l@ill.fr Subject: Quantitative analysis Dear all, I have this question, I have been refined one mixture (of well-know percentage composition) of CaCO3, CaF2, SiO2 and Al2O3, with preferential orientation in CaCO3 (104) and CaF2 (111) with good results. When I add to the mixture FeCO3 and I refine with preferential orientation (104), it happens that when I don´t apply the preferential orientation in all this phases, I have correct values of percentage composition, but when I apply the preferential orientation the refinement is good but with incorrect values of percentage composition. This experiment has been taken in Bragg Brentano geometry. How I should refine this mixture? Thanks a lot by your help. Mario Macías Universidad Industrial de Santander Colombia
RE: Quantitative analysis
Spinning the sample doesn't reduce preferred orientation much. It does, however, improve ones counting statistics very nicely. Martin M Vickers Dept. of Chemistry UCL 20, Gordon Street London WC1E 0HX Subject: RE: Quantitative analysisDate: Tue, 28 Oct 2008 09:25:13 -0500From: [EMAIL PROTECTED]: rietveld_l@ill.fr I am learning QPA and am worried about PO. I wonder why sample spinning isn’t discussed more. I am luckily able to barrow time on a newer diffractometer with a sample spinner. Does this reduce PO? Or completely eliminate it? There is a set up variable in GSAS for whether you are spinning the sample – are there guidelines for how many revolutions to spin the sample if you just want to reduce PO? Thanks to all for there help!!! Blaise * * * * * * * * * * * * * Blaise Mibeck Research Scientist Energy Environmental Research Center University of North Dakota 15 North 23rd Street, Stop 9018 Grand Forks, ND 58202-9018 Phone: (701) 777-5077 Email: [EMAIL PROTECTED] _ Discover Bird's Eye View now with Multimap from Live Search http://clk.atdmt.com/UKM/go/111354026/direct/01/
RE: Quantitative analysis
Hi Blaise In Bragg-Brentano mode, sample spinning does nothin for PO. This is because the diffraction vector is normal to the sample surface, and sample spinning rotates along this vector. Spinning does increase your particle statistics, which almost always helps. If you're looking at a capillary, spinning the capillary does help with PO, but just being in a capillary helps PO. As to spinning speeds, a good guide is one revolution per data point. Cheers Matthew Matthew Rowles CSIRO Minerals Box 312 Clayton South, Victoria AUSTRALIA 3169 Ph: +61 3 9545 8892 Fax: +61 3 9562 8919 (site) Email: [EMAIL PROTECTED] From: Mibeck, Blaise [mailto:[EMAIL PROTECTED] Sent: Wednesday, 29 October 2008 01:25 To: rietveld_l@ill.fr Subject: RE: Quantitative analysis I am learning QPA and am worried about PO. I wonder why sample spinning isn't discussed more. I am luckily able to barrow time on a newer diffractometer with a sample spinner. Does this reduce PO? Or completely eliminate it? There is a set up variable in GSAS for whether you are spinning the sample - are there guidelines for how many revolutions to spin the sample if you just want to reduce PO? Thanks to all for there help!!! Blaise * * * * * * * * * * * * * Blaise Mibeck Research Scientist Energy Environmental Research Center University of North Dakota 15 North 23rd Street, Stop 9018 Grand Forks, ND 58202-9018 Phone: (701) 777-5077 Email: [EMAIL PROTECTED]mailto:[EMAIL PROTECTED] -Original Message- From: David L. Bish [mailto:[EMAIL PROTECTED] Sent: Tuesday, October 28, 2008 9:09 AM To: Martin; [EMAIL PROTECTED]; rietveld_l@ill.fr Subject: RE: Quantitative analysis I agree that it's always best to avoid preferred orientation, but that is easier said than done on a routine basis. I have personally had good luck with the M-D PO correction on many known samples, as long as the PO was not severe. However, I imagine that Mario's problems are related to microabsorption in this case. Mario, if you can re-measure your data with a Co or Fe tube, it would be a good test of this. Dave Bish At 08:51 AM 10/28/2008 -0400, Martin wrote: Sorry to disagree. Experience tells me otherwise - the March-Dollase correction has nearly always led to poor quant results for me. It most certainly cannot be applied safely. Martin -- M Vickers Dept of Chemistry UCL Subject: Re: Quantitative analysis Date: Tue, 28 Oct 2008 02:53:20 -0700 From: [EMAIL PROTECTED] To: Rietveld_l@ill.fr Dear Mario, One more possible problem of applying preferred orientation corrections in QPA is that not all of them are normalized. For example, the March-Dollase correction is normalized and can be applied safely, but the Rietveld-Toraya correction is inapplicable to QPA as it does not preserve the scale normalization. Best regards, Leonid *** Leonid A. Solovyov Institute of Chemistry and Chemical Technology K. Marx av., 42 660049, Krasnoyarsk Russia Phone: +7 3912 495663 Fax: +7 3912 238658 www.icct.ru/eng/content/persons/Sol_LAhttp://www.icct.ru/eng/content/persons/Sol_LA For the best free wallpapers from MSN Click here!http://wallpapers.msn.com/?ocid
RE: Quantitative analysis
Dear Mario, If the quantity of FeCO3 appears to be smaller than the actual value, then it could be due to absorption. If you are using a copper source (CuKalpha) then that excites iron fluorescence, which is radiated equally in all directions... this means that the beam does not penetrate the FeCO3 particles entirely, and results in incomplete diffraction from these particles. There are programs that correct for this problem, but as far as I know there is no freeware to deal with this effect. - Kurt * Kurt Leinenweber Dept. of Chemistry and Biochemistry Arizona State University Tempe, AZ 85287-1604 phone (480)-965-8853 fax (480)-965-2747 *** -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Monday, October 27, 2008 8:48 AM To: Rietveld_l@ill.fr Subject: Quantitative analysis Dear all, I have this question, I have been refined one mixture (of well-know percentage composition) of CaCO3, CaF2, SiO2 and Al2O3, with preferential orientation in CaCO3 (104) and CaF2 (111) with good results. When I add to the mixture FeCO3 and I refine with preferential orientation (104), it happens that when I don´t apply the preferential orientation in all this phases, I have correct values of percentage composition, but when I apply the preferential orientation the refinement is good but with incorrect values of percentage composition. This experiment has been taken in Bragg Brentano geometry. How I should refine this mixture? Thanks a lot by your help. Mario Macías Universidad Industrial de Santander Colombia
RE: Quantitative analysis
Dear Mario, My experience of quant Rietveld is much the same as yours - poor quant result if using any sort of PO function. Advise as others have here - reduce PO. Capillary geometry may help in many instances but in this case could then have problems with absorption seeing as you will most likely be having to use Co radiation to avoid fluorescence from the iron. Good luck, Martin _ Win an Xbox 360 or £200 Top Shop Vouchers http://clk.atdmt.com/GBL/go/115454062/direct/01/
