Dear all,
I think the statement that one cannot do line-profile analysis using GSAS is too strong. In principle it is possible to do some size strain analysis using GSAS, if the instrumental profile is e.g. sufficiently described previously by the Thompson-Cox-Hastings (TCH) profile function (includes measuring corresponding data on a suitable standard). I think, even involvement of the Finger asymmetry correction does not introduce systematic errors. Then the increase in the tantheta and 1/costheta related Gaussian and Lorentzian line width components of the TCH description upon Rietveld refinement on the basis of diffraction data exhibiting physical line broadening can in principle be associated with microstrain- and size-related quantities. This can also be extended by involving anisotropic size and microstrain models. Thus, on this level of line broadening analysis, everything neccessary is contained in GSAS. Of course, something like microstrain and size distributions cannot be obtained using GSAS. Of course there are problems: 0. Microstrain broadening must be proportional to tan(theta). This is not neccessarily the case. There mustn't be further line broadening contributions like stacking faults, complicating the situation. 1. If both size and strain contributions are present, one most be aware of the correlation between the tantheta and 1/costheta dependent compontents. 2. One has to be aware to which average values of the size and microstrain distributions the increases of the line width parameters can be associated with. This requires for GSAS a close analysis of the GSAS manual (how are the line-width paramerters defined!) and line broadening literature, how such pseudo-Voigt line width parameters can be related with averages microstructure parameters. Thus it is not made easy for the user to extract something like that from the line width parameters. But perhaps it is better that way, because consequently the user is forced to to deal himself with the required theory, rather than just refining a parameter called size and one called microstrain, believing in the results and publish the values.... Definitely there are much better procedures to analyse size and microstrain than by GSAS. So, going to the problem of Apu: If the instrumental profile is well described before using TCH, refinement of (only) LX (and perhaps P) gives you quantities whiuch you should be able to relate to size related quantities upon reading the GSAS manual and some line broadening literature. Best regards Andreas Leineweber > Dear Prof. Lutterotti, > I was also aware of the fact that GSAS is not made for Size Strain analysis. I got interested to use the Size strain refinement feature of GSAS only after going through the article : > "Size-strain line broadening analysis of the ceria round-robin sample" by Prof. D. Balzar et. al. Journal of Applied Crys. 37(2004)911-924. > > In that round robin results they have reported the size strain obtained from GSAS. > > I my case also when I am trying with GSAS, the diffraction pattern is fitting well except the peak braodening. I think this brodening is due to small domain size effect. I that case how will I obatin a good fit with GSAS. > > Thanking you. > > 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 > /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/ > > > ----- Original Message ----- > From: Luca Lutterotti <[EMAIL PROTECTED]> > Date: Friday, March 25, 2005 3:31 pm > > > Dear Apu, > > > > I know I will start up a "good" debate here, but size-strain > > analysis > > with GSAS is a non-sense. The program was not written with that > > purpose > > in mind and in fact it does not contains the instrumental > > aberration > > part of the broadening that is necessary for such computation. > > Indeed it is possible to get at end some size-strain data, but > > quite > > hard as you have to do all correction later and out of the > > program. So > > it is like using GSAS for peak fitting, so better to use a peak > > fitting > > dedicated program. > > > > Best wishes, > > Luca Lutterotti > > > > On Mar 25, 2005, at 7:15, [EMAIL PROTECTED] wrote: > > > > > Dear All, > > > I am trying to perform Rietveld refinement on a very simple > > system > > > using GSAS. I have obtained a reasonable fit except the peak widths. > > > > > > I want to use the size and strain refinement option in GSAS to > > make > > > the fit well. > > > > > > Please tell me how to use the SIZE STRAIN refinement option in GSAS. > > > > > > P.S. I am using the EXPGUI. > > > > > > > > > Thanks in advace. > > > > > > 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 > > > /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/ > > > > > > > > > @
