Dear Darin,
Darin Hoffman wrote:
To
any one that can help:
I am performing a rietveld refinement using GSAS on x-ray data of a rod
material. I have thus far been able to make a good fit by simply
attaining the Particle size and strain broadening. The data so far
matches close to what I expect. I am using the type 2 pseudo-Voigt
profile and have been trying to refine my fit with as few variables as
possible. I have just recently started using the GSAS program so I
have tried to use only the variables I know well. Mainly the size and
strain parameters. I tried for my own curiosity to refine the Gamma
variables (Gamma11,22,33,12,13,23). This has improved my refinement to
a Rwp=0.14 rather than a Rwp=0.3. Since this has improved my fit I
think I am using the variables correctly. So my question is:
1) What is the physical representation of these variables the gamma
variable? The GSAS manual describes them as the empirical extension of
the microstrain anisotropy. I know that they put weighting on the
(h,k,l) coordinates to deal with line broadening but how do I know they
are weighting them correctly for my hexagonal lattice?
2)From the GSAS manual (gamma=y):
yl=y11(h^2)+y22(k^2)+y33(l^2)+2*y12(hk)+2*y13(hl)+2*y23(kl)
What does this equation mean?
This type of anisotropy of microstrain was initially introduced
empirically. However, there are also physically relavant cases which
should give this line broadening. See also in
J. Appl.
Crystallogr. 37 (2004) 123ff for this and the relation of this function
to the Stephens model Peter pointed at.
--
Dr. Andreas Leineweber
Max-Planck-Institut fuer Metallforschung
Heisenbergstrasse 3
70569 Stuttgart
Germany
Telephone: +49 (0)711 689 3365
Telefax: +49 (0)711 689 3312
[EMAIL PROTECTED]
http://www.mf.mpg.de/de/abteilungen/mittemeijer/english/index_english.htm
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