[GSAS-II] Different profiles for different phases

[Arianna Lanza]

Dear Bartłomiej,

From my intuitive understanding of GSAS-II, I think that the approach suggested is that you fit one profile function only because it is ideally supposed to be the pure instrumental profile determined from a standard. Then you will model deviations from the instrumental profile by using some of the many broadening models available in the <Data> tab of each phase (domain size model, mustrain model etc). (This names suggest that anything differing from the pure instrumental profile is treated as if coming from the microstructure of the phase, but obviously the refined values of these models are only physically meaningful under certain conditions).

For example you could use the Be substrate also as an internal peak shape standard, fit the profile from its peaks only, and then keep it fixed. Finally you refine the broadening parameters for the sample phase using the domain size model, mustrain model etc.

Kind regards,

Arianna




-----Original Message-----
From: Bartłomiej Gędziorowski <gedzior at agh.edu.pl> 
Sent: Friday, September 6, 2019 14:09
To: gsas-ii at aps.anl.gov
Subject: [GSAS-II] Different profiles for different phases

Hello Everybody,

first of all I'd like to say hello to everybody, because this is my first post in this list. My name Is Bartłomiej Gędziorowski, I work at AGH UST in Cracow, Poland and I'm a materials scientist.

I worked few years with GSAS+EXPGUI, now from some time I'm migrating to GSASII and I cannot find one feature. It is the setting of different profile sets for different phases for a single histogram. I have a sample in form of a thin layer on a beryllium substrate. As a result on diffractograms I can see both my material reflections, quite wide because of sub-micron grains, and very thin beryllium. This causes a problem, because I cannot find suitable set of profile values for double-phase refinement. I worked it around putting beryllium reflections in the background, but that's not a good solution for me. 
The beryllium peaks are very helpful, because they allow to precisely fit sample displacement - we use special in-situ cell in which placing sample in right position is challenging and we always have some shift. 
For that reason it would be perfect to do a double-phase fit.

I would be grateful for some suggestions how to solve my issue.

Best regards,

--
Bartłomiej Gędzioroski, Ph.D.
AGH University of Science and Technology, Faculty of Energy and Fuels, Department of Hydrogen Energy, al. Mickiewicza 30
30-059 Krakow, Poland