Re: rietveld refinement
methodology, if not that they are physical (I believe they are physical in case of size-only effect). The diffraction alone can not decide. Significantly different physical size distributions could describe equally well the peak profile (J.Appl.Cryst. v35 (2002) 338-346 - self citation too). Nicolae Popa
RE: Unexpected honour
Seriously Thanks guys I did not know about this site till I retired and have wished I knew a lot earlier. Try also the dissident SDPD Mailing List : Why dissident Armel ? I am happy to see that you are still a member of the Rietveld list and still use ICSD, but if your are trying for an English title, using these to construct dissident alternatives doesn't seem quite cricket :-) Especially in reply to a very welcome compliment to the Rietveld list. Thanks Laurie. Alan. Alan Hewat, ILL Grenoble, FRANCE [EMAIL PROTECTED] fax (33) 4.76.20.76.48 (33) 4.76.20.72.13 (.26 Mme Guillermet) http://www.ill.fr/dif/AlanHewat.htm ___
Bond angle and bond length
Hi, I am using FULLPROF program code for Rietveld refinement of XRD data. I don't know how to obtain values of bond angles and bond lengths by refinements, or some reliable freeware available to calculate. Please suggest. Krushna
Re: rietveld refinement
The diffraction alone can not decide. Significantly different physical size distributions could describe equally well the peak profile (J.Appl.Cryst. v35 (2002) 338-346 - self citation too). Nicolae Popa Looking at your figures 6b1 and 6b2, I measure how we differ on the sense of significantly different. As you comment in the text, The curves 1 and 2 differ in the position of the maximum by only 2 A and in height of the maximum by 9.76%. I would not call that significantly different but very similar. Armel
RE: Unexpected honour
Why dissident Armel ? I am an adept of the open access to the knowledge, your religion looks different. Armel from http://www.dictionary.com: Disagreeing, as in opinion or belief. \Dissi*dent\, a. [L. dissidens, -entis, p. pr. of dissidere to sit apart, to disagree; dis- + sedere to sit: cf. F. dissident. See http://dictionary.reference.com/search?q=sitSit.] No agreeing; dissenting; discordant; different Our life and manners be dissident from theirs. --Robynson (More's Utopia). \Dissi*dent\, n. (Eccl.) One who disagrees or dissents; one who separates from the established religion. The dissident, habituated and taught to think of his dissidenc? as a laudable and necessary opposition to ecclesiastical usurpation. --I. Taylor. adj 1: characterized by departure from accepted beliefs or standards [syn: http://dictionary.reference.com/search?q=hereticalheretical, http://dictionary.reference.com/search?q=heterodoxheterodox] 2: disagreeing, especially with a majority [syn: http://dictionary.reference.com/search?q=dissentientdissentient, http://dictionary.reference.com/search?q=dissenting%28a%29dissenting(a)] n : a person who dissents from some established policy [syn: http://dictionary.reference.com/search?q=dissenterdissenter, http://dictionary.reference.com/search?q=protesterprotester, http://dictionary.reference.com/search?q=objectorobjector, http://dictionary.reference.com/search?q=contestantcontestant] http://dictionary.reference.com/search?q=00-database-infodb=wnSource: WordNet ® 2.0, © 2003 Princeton University
RE: Unexpected honour
I have no other choice but to use ICSD if I pretend to be an expert/wizard (=adept ??) in inorganic chemistry. Armel, that is the nicest compliment I have ever heard about ICSD. Sincerely, Thanks ! Alan xxx See how we are different. For you this is a compliment. For me no other choice is an intolerable constraint. No thanks ! Armel
Re: rietveld refinement
The diffraction alone can not decide. Significantly different physical size distributions could describe equally well the peak profile (J.Appl.Cryst. v35 (2002) 338-346 - self citation too). Nicolae Popa Looking at your figures 6b1 and 6b2, I measure how we differ on the sense of significantly different. As you comment in the text, The curves 1 and 2 differ in the position of the maximum by only 2 A and in height of the maximum by 9.76%. I would not call that significantly different but very similar. Armel Yes, but the figure 6b represents the COLUMN LENGTH distribution not the CRYSTALLITE RADIUS distribution (in this case of spherical crystallites). The crystallite radius distributions are given in 6a1 and 6a2 (lognormal and gamma, respectively) and they are significantly different, what can be seen also in the table 1: the average radius and the dispersions are completely different. Nevertheless the profile of the diffraction peak is equaly well described. And the column length distribution is quite the same (as discussed in text and as you observed). But when we are speaking about the physical model we understand in fact the distribution of the crystallite radius (if spherical). Is that lognormal or gamma? Is the average radius 90(6) or 69(1) Angstroms, is the parameter c (determining the dispersion) 0.18 or 0.39? We can not say only from diffraction that one is more physical than other. On the other hand is the column length distribution a full physical description of the crystallites, I mean of the shape and radius (radii) distribution? I think not. You can imagine, for example, that the crystallites are even not spherical, but ellipsoidal. It is easy to understand that if the Euler angles representing the orientations of the ellipsoidal principal axes with respect to the crystal axes are UNIFORMLY distributed in their domains of definition, will be NO anisotropy effect. Then we can think the crystallite are spherical with a certain distribution of radius, when in fact they are ellipsoidal with other distributions of (three) radii. But the column length distribution (and the peak profile) is the same. What we see in diffraction is the column lengths (volume area averaged) and the classics were not full ignoring the shape and radius (radii) distribution(s). Nicolae Popa (Mister, Messieur, Don, Dom, etc.)
Re: Unexpected honour
- Why dissident Armel ? I am an adept of the open access to the knowledge, your religion looks different. Armel from http://www.dictionary.com: Disagreeing, as in opinion or belief. \Dissi*dent\, a. [L. dissidens, -entis, p. pr. of dissidere to sit apart, to disagree; dis- + sedere to sit: cf. F. dissident. See http://dictionary.reference.com/search?q=sitSit.] No agreeing; dissenting; discordant; different Our life and manners be dissident from theirs. --Robynson (More's Utopia). \Dissi*dent\, n. (Eccl.) One who disagrees or dissents; one who separates from the established religion. The dissident, habituated and taught to think of his dissidenc? as a laudable and necessary opposition to ecclesiastical usurpation. --I. Taylor. Sorry, but I think there is here a mal interpretation (is correct that in English?) of the dictionary. I don't think that the people in SDPD list are thinking the powder diffraction differently than the people in the Rietveld list. Or, if there are differences on some particular subject from one member to other, this can happen also inside the same chat list. An alternative, a diversification, does not mean automatically a disidence. Let us not blurred a word very dear to people like me, rising and living most of the life in a dictatorial regime. Yours, Nicolae Popa
Re: rietveld refinement
What we see in diffraction is the column lengths (volume area averaged) and the classics were not full ignoring the shape and radius (radii) distribution(s). Nicolae Popa (Mister, Messieur, Don, Dom, etc.) Of course I agree with you that completely different shapes may correspond to the same distribution of column length. For diffraction, and considering one direction, the columns of cells look exactly as if they were separated. So, obviously : |--| | |--| | | |--|--| |--|--|--|--| gives the same column length distribution as : |--| | | |--| | |--|--| | |--|--|--|--| or as separated columns : |--| [--| | | | | | | | | |--| |--| |--| |--| |--| |--| or etc, taking the columns in the bottum-up sense. But, with these 3 different models (and more are possible), you would not have the same distribution of column lengths in the orthogonal direction... My problem with most recent papers about size effect is that they always consider cubic compounds, possibly spherical crystallites etc. In such a case, all directions are gathered in one. Could you study something more complex sometimes ? In my self-citation work, the study was made on nickel hydroxyde, with hexagonal structure, looking for columns exclusively in the direction of the c axis, using the Bertaut formulations, with careful extraction of the column lenght distribution after deconvolution from the instrumental effect. There was a strong size anisotropy. The X-ray study cannot gives the shape (you see that I agree with you on that point), an electron microscopy study showed that the coherently diffracting domains are plate-like crystallites aggregated along the c axis. 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 profiles. You would have maybe to restrain to the consideration in one direction : if no change is produced in all other directions, what is the degree of freedom for the crystallite shape now ? Is it possible to organize the columns differently in one direction without changing also the peak profiles in all other directions for a triclinic compound ? 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 ;-). Best Armel
JOB: Instrument scientist for the high resolution powder
Hahn Meitner Institute, Berlin Department of Magnetism Scientist Ph.D. (Physicist, Chemist) No. SF 2004/16 The Hahn-Meitner-Institut invites applications for a postdoctoral position in the area of neutron powder diffraction. The successful candidate will be the responsible scientist for the high resolution powder diffractometer, E9, at the Berlin Neutron Scattering Center (BENSC). The Hahn-Meitner-Institut is a German National Laboratory and a member of the Hermann von Helmholtz Association of National Research Centres and has about 850 employees. It hosts the Berlin Neutron Scattering Center (BENSC) (http://www.hmi.de/bensc/ http://www.hmi.de/bensc/ ), a user facility open to scientists from all over the world. To probe the structure and dynamics of solids and liquids, BENSC provides the national and international research community with state-of-the-art neutron scattering equipment and expertise. The successful candidate will develop neutron scattering instrumentation and techniques, and will support BENSC users on the E9 high resolution powder diffractometer. He/she is also expected to participate in an existing research program on strongly correlated transition metal oxides. A broad knowledge in condensed matter physics will be required as well as experience in neutron scattering instrument development and operation. A background in neutron diffraction, the Rietveld method, crystallography and a strong scientific interest in transition metal oxide physics will be strongly preferred. The successful candidate will have access and is expected to utilize for his/her own research excellent sample preparation facilities that include oxide powder synthesis labs (with high temperature variable atmosphere furnaces), and a floating zone optical mirror furnace for single crystal growth. Standard sample characterization facilities are also available (XRD, SQUID, specific heat). Staff at BENSC have access to 25% of the beam time on all neutron scattering instruments for their own research. The appointment is for 3 years and is renewable for another 2 years. The salary is in the range of 36.000 40.000 EUR per annum depending on age. Applicants should send a letter of application, a detailed CV, a list of publications, and copies of degrees to Hahn-Meitner-Institut Berlin, Abt. Personal und Soziales, Glienicker Str. 100, D-14109 Berlin, Germany before 12 December 2004 quoting reference No. SF 2004/16. For informal inquiries, please contact Dr. D. Argyriou (phone +49-30-8062-3016, email [EMAIL PROTECTED] mailto:[EMAIL PROTECTED] ) or Dr. H.A. Graf (phone +49-30-8062-2778, e-mail [EMAIL PROTECTED]).
Re: rietveld refinement
Small error, sorry, three of the possible arrangement were : |--| | |--| | | |--|--| |--|--|--|--| |--| | | |--| | |--|--| | |--|--|--|--| |--| | | |--| | | | | |--| |--| |--| |--| |--| |--| Armel
diffraction software survey
Dear colleagues, enclosed is your feedback to the Rietveld-list survey on powder diffraction software usage/preferences, which was conducted Nov 2003. Your replies were very helpful, as we are working on a detailed scope of diffraction software to be developed under the proposed DANSE project. We have received 31 email replies to the survey, but we would like to reach a wider community. In order to do that, we have recreated this survey online at http://danse.cacr.caltech.edu/polls/survey.php?sid=22 We would really appreciate if you could fill out this survey and help us determine the software needs of the diffraction community. Those of you who have already submitted email replies don't need to do that; we will re-enter your replies for you. Thanks, Simon J.L. Billinge, Pavol Juhas PS: If you want to learn more about the DANSE project, please visit http://wiki.cacr.caltech.edu/danse/index.php/Main_Page Results of Rietveld email-list survey from 2003-11-11 conducted on software preferences and usage of the powder diffraction community. COUNTRY: UK 7/31 (23%) USA 6/31 (19%) France 6/31 (19%) Germany 4/31 (13%) Italy 2/31 (6%) Switzerland 1/31 (3%) Portugal1/31 (3%) Norway 1/31 (3%) India 1/31 (3%) Canada 1/31 (3%) Austria 1/31 (3%) AFFILIATION TYPE Academia 21/31 (68%) National lab9/31 (29%) Other institution 2/31 (6%) Industry1/31 (3%) TYPE OF POWDER DIFFRACTION INSTRUMENTS USED In-house x-ray 28/31 (90%) Synchrotron x-ray 22/31 (71%) Reactor neutrons 14/31 (45%) Spallation neutrons14/31 (45%) POWDER DIFFRACTION SOFTWARE USED FOR --- Rietveld refinement: 31/31 (100%) --- GSAS 28/31 (90%) FullProf 11/31 (35%) TOPAS 4/31 (13%) FullProf/WinPlotr 2/31 (6%) Rietica 2/31 (6%) CCSL codes 1/31 (3%) DBWS94111/31 (3%) Materials Studio1/31 (3%) MAUD1/31 (3%) MPRODD 1/31 (3%) Rietan 1/31 (3%) WinCSD 1/31 (3%) WinMProf1/31 (3%) --- Peak indexing/unit cell determination: 29/31 (94%) --- Crysfire 14/29 (48%) Dicvol 7/29 (24%) TREOR 6/29 (21%) ITO 3/29 (10%) Stoe WinXPow2/29 (7%) UFIT2/29 (7%) WinPlotr2/29 (7%) CheckCell
