Re: Zero shift vs sample shift
Peter Y. Zavalij ( (no email) )
Wed, 25 Mar 1998 10:17:51 -0500
>
>I fully agree with you that sample height is the one parameter to refine
>and that and that this parameter has a rather different angular
>dependence. However, in agreement with Rory experience we are never able
>to refine sample height in Bragg-Brentano geometry on the Siemens D5000
>with alpha1. We found that the correlation between those parameters was
>always close to 100%. And yes this is with data collected up to 120 deg 2
>theta. By the way how do you model your asymmetric peak shapes? I allways
>find that this parameter in the peak profile correlates highly with all
>the parameters mentioned earlier, including the lattice parameters.
>
>
>Jaap Vente
>
I never refine zero and sample shift because I do believe that zero shift
has to be 0 on modern diffractometers but I do refine sample shift and
beam penetraiting simultaneously because of low absorbtion of our
samples. The asymmeric parameters (I am useng GSAS or my own
software with the same asymmetric function) can be refined simultanuosly
only on the final stages when R-factors are low. I also refine all three
angular corrections simultaneosly but only on LaB6 standard after
diffractometer's alligment to make sure that ZERO shift is 0. It does correlate
but is refineable.