[GSAS-II] Pawley refinemet question

[Toby, Brian H.]

Hi Sergey,

   Both LeBail and Pawley fits are not able to determine phase fractions because the scale factors are all arbitrary and thus the phase fractions cannot be refined. However, the reported mass/weight fractions are determined from the unrefined phase fractions and they are displayed even though meaningless.

Brian

On Apr 8, 2020, at 12:58 PM, Sergey Ushakov via GSAS-II <gsas-ii at aps.anl.gov<mailto:gsas-ii at aps.anl.gov>> wrote:

Greetings! I have a question maybe not specific to GSAS-II but more about Pawley vs Le Bail fitting of powder XRD data.
I work on high temperature data from laser-heated solid spheroids which rotate in a gas flow in aerodynamic levitator.
The data are collected in transmission geometry at 6-ID-D at APS.
The rotation is not well controlled since it depends on the shape of each bead formed by melt solidification, i.e., on surface tension, volume change on melting, etc.
So, sometimes data are very much powder-like and amenable to Rietveld refinement of the structure, but sometimes they are not, and in this case, I do Pawley fit for cell parameters.
I used to do Le Bail fitting for that in GSAS-I, but I understand that it was replaced by Pawley refinement (although there is an option for Le Bail extraction of intensities?).

To my surprise, Pawley fit in GSAS-II yield phase/weight fraction if one turns it on for refinement.
I thought phase fraction could be correctly refined only from Rietveld?

I would appreciate any comments on this!

Sergey

--
Sergey Ushakov PhD

Staff Research Associate

Peter A Rock Thermochemistry Laboratory and NEAT ORU
Rm 4415, Chemistry Annex
University of California, Davis
Davis, CA 95616

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