Hi!
I am trying to refine some XRD data using GSAS and looking for an
instrument parameter file for the Rigaku Dmax 2000 x-ray diffractometer.
Can anyone help?
Thanks Donna
Donna (and anyone else who wonders about this),
In gsas\examples there is an iparm file (inst_xry.prm) that can be used for most any
Bragg-Brentano powder diffractometer. These instruments all perform more or less
equally independent of manufacturer with respect to the things of interest for
Your sample will probably broaden the lines (LX, LY, etc.) so much that
any attempt to vary the Gaussian
coefficients will yield nonsense.
Just some remark (of course, I am not a great specialist):
At least to my experience, there is always some Gaussian broadening from
the sample as well, and
U, V, and W tend to be highly correlated
The correlation between U,V,W is the result of a resolution curve that doesn't have a
well defined minimum. If you differentiate the Caglioti equation for the FWHM:
FWHM**2=U.tan**2(theta)+V.tan(theta)+W
you obtain the condition for the minimum as
Theoretically U,V,W should not be refined at all as they describe instrumental
broadening, and this is exactly what I do
(usually). After diffractometer alignment, a good quality pattern in whole possible
angular range has to be collected from Rietveld
standard which currently is LaB6. From
Theoretically U,V,W should not be refined at all as they describe instrumental
broadening
This is true only when there is no Gaussian strain present.
Brian
