RE: Rietveld: U,V,W
Brian wrote: >U and W should be instrumental constants that will not change with >sample, >while V can have both an instrumental and a >residual stress component. Maxim wrote: >as far as I understand, the strain broadening term should have FWMM~theta >>dependence, i.e. Lorentzian Y in "standard" (GSAS) notation. >For the Gaussian part you have >FWHM^2=U*tan^2(th)+V*tan(th)+W+P/cos^2(th) >and the term that varies roughly as ~theta is U, not V. >Therefore, based on that and probably erroneously, I used to refine U >>parameter rather than V (+ P, X, Y, of course). >I am wondering if somebody could make this more clear? Dear Brian and Maxim, In fact, the term responsible for the Gaussian strain component is U, not V. 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 ***
RE: Rietveld: U,V,W
Dear colleagues, one question on that: >U and W should be instrumental constants that will not change with sample, while V can have both an instrumental and a >residual stress component. as far as I understand, the strain broadening term should have FWMM~theta dependence, i.e. Lorentzian Y in "standard" (GSAS) notation. For the Gaussian part you have FWHM^2=U*tan^2(th)+V*tan(th)+W+P/cos^2(th) and the term that varies roughly as ~theta is U, not V. Therefore, based on that and probably erroneously, I used to refine U parameter rather than V (+ P, X, Y, of course). I am wondering if somebody could make this more clear? >FullProf might be a bit more stable, but I think the process there is about the same. (BTW, if anyone works out how to >convert GSAS profile terms to ones used in FullProf, I'd be interested to get those relationships into CMPR; I am not sure >if the scaling is only between centidegrees**2 and degrees**2.) So far I noticed that Fullprof uses interchanged (v.r.t. GSAS) XY, i.e. X corresponds to strain term there. There might be also other differences, of course... Sincerely, Maxim. From: Brian H. Toby [mailto:[EMAIL PROTECTED] Sent: Monday, December 01, 2008 5:21 AM To: May, Frank Cc: rietveld_l@ill.fr Subject: Re: Rietveld: U,V,W What is the correct procedure for refining U,V,W? It is my understanding that those parameters are a function of instrument geometry. Does one use a standard material to determine U,V,W and then fix their values for the instrument you're using?or do the values of U,V,W change depending on the sample being examined? If so, why do the values change? The GSAS manual covers the latter part of you questions pretty well, though perhaps indirectly. In theory, U and W should be instrumental constants that will not change with sample, while V can have both an instrumental and a residual stress component. However, this assumes that one also refines a crystallite size parameter, P when needed, which many people (myself included) do not. In that case, U, V & W will all change to compensate for crystallite broadening. I do recommend using a standard with good sharp peaks (SRM LaB6 is the ideal, though there are likely to be many other oxides handy that work reasonably.) If you can't get a good fit to your standard, then you do not want to advance to an unknown until you understand the problems with your instrument/technique. Where possible, I try to start a refinement with values that are close to correct for U, V & W (+ X & Y where significant) and put off refining them until late in the refinement, when they tend to be pretty stabile. Initially, I usually refine U, V & W together and then refine X and then Y solo and then finally in combinations until everything is refined together. Look for parameters that are refining to zero and turn them off, since GSAS does not deal with that very well. Also look at the widths vs 2theta (widplt) to see if the functions are reasonable. The routine in CMPR for fitting U, V & W values to a set of peak widths has been useful for me where I don't have good calibration information for an instrument. FullProf might be a bit more stable, but I think the process there is about the same. (BTW, if anyone works out how to convert GSAS profile terms to ones used in FullProf, I'd be interested to get those relationships into CMPR; I am not sure if the scaling is only between centidegrees**2 and degrees**2.) Brian Brian H. Toby, Ph.D.office: 630-252-5488 Materials Characterization Group Leader, Advanced Photon Source 9700 S. Cass Ave, Bldg. 433/D003 work cell: 630-327-8426 Argonne National Laboratory secretary (Marija): 630-252-5453 Argonne, IL 60439-4856 e-mail: brian dot toby at anl dot gov
Re: Rietveld: U,V,W
Why my reply went to the author's personal mail box? I am very sorry for that. Now I am hunting for a standard reference material to determine the profile parameters of our instrument X'pert Pro. -- 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: Rietveld: U,V,W
What is the correct procedure for refining U,V,W? It is my understanding that those parameters are a function of instrument geometry. Does one use a standard material to determine U,V,W and then fix their values for the instrument you're using?or do the values of U,V,W change depending on the sample being examined? If so, why do the values change? The GSAS manual covers the latter part of you questions pretty well, though perhaps indirectly. In theory, U and W should be instrumental constants that will not change with sample, while V can have both an instrumental and a residual stress component. However, this assumes that one also refines a crystallite size parameter, P when needed, which many people (myself included) do not. In that case, U, V & W will all change to compensate for crystallite broadening. I do recommend using a standard with good sharp peaks (SRM LaB6 is the ideal, though there are likely to be many other oxides handy that work reasonably.) If you can't get a good fit to your standard, then you do not want to advance to an unknown until you understand the problems with your instrument/technique. Where possible, I try to start a refinement with values that are close to correct for U, V & W (+ X & Y where significant) and put off refining them until late in the refinement, when they tend to be pretty stabile. Initially, I usually refine U, V & W together and then refine X and then Y solo and then finally in combinations until everything is refined together. Look for parameters that are refining to zero and turn them off, since GSAS does not deal with that very well. Also look at the widths vs 2theta (widplt) to see if the functions are reasonable. The routine in CMPR for fitting U, V & W values to a set of peak widths has been useful for me where I don't have good calibration information for an instrument. FullProf might be a bit more stable, but I think the process there is about the same. (BTW, if anyone works out how to convert GSAS profile terms to ones used in FullProf, I'd be interested to get those relationships into CMPR; I am not sure if the scaling is only between centidegrees**2 and degrees**2.) Brian Brian H. Toby, Ph.D.office: 630-252-5488 Materials Characterization Group Leader, Advanced Photon Source 9700 S. Cass Ave, Bldg. 433/D003 work cell: 630-327-8426 Argonne National Laboratory secretary (Marija): 630-252-5453 Argonne, IL 60439-4856 e-mail: brian dot toby at anl dot gov
Rietveld: U,V,W
To all: What is the correct procedure for refining U,V,W? It is my understanding that those parameters are a function of instrument geometry. Does one use a standard material to determine U,V,W and then fix their values for the instrument you're using?or do the values of U,V,W change depending on the sample being examined? If so, why do the values change? Thanks in advance. Frank May From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Sun 11/30/2008 1:32 PM To: rietveld_l@ill.fr Subject: 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/
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.)
