[GSAS-II] Standard deviations on lattice parameters

[Anselm Loges]

Hi there,

I am afraid I have a bit of a dumb question. I am fitting lab-XRD powder
data of topaz. The interesting thing going on with topaz is the F/OH ratio
(all on a single lattice site). Now, trying to refine the position
occupation with F or O from such data is obviously, let's say,
challenging. Fortunately, there is a well documented relationship between
the b lattice parameter and the F/OH ratio, allowing us to determine the
ratio much more precisely than by trying to optimize the occupation ratio
directly. That also means, we could use the peak broadening that is caused
by variance in the b length as a measure of chemical zonation in F/OH
ratio in the sample powder. But for some reason I cannot find the standard
deviation of the lattice parameters in the output data or in the user
interface. Where are they?

On a related, less silly note: Is it possible to correlate the occupation
ratio with a lattice parameter? I cannot find a way to do that either. It
is not super important since just setting the occupation to whatever,
optimizing the unit cell, and then manually feeding the resulting F/OH
ratio back into the site occupation seems to work well enough in this
case. Just thought that if this feature does not exist, I'd like to submit
a feature suggestion for future versions. This may be more relevant with
more complicated structures.

Thanks and cheers,
Anselm





--------------------------------------------
Wiss. Mitarbeiter / Postdoc
SFB1349 "Fluor-Spezifische Wechselwirkungen"
Freie Universität Berlin
Arbeitsbereich Mineralogie-Petrologie
Malteserstr. 74-100
Ge­bäude N, Raum N 26
12249 Berlin
Tel: +49 30 838 666 39