[GSAS-II] Peaks Profile Parameters

[Leopoldo Suescun]

Dear Emily,

If you have collected one dataset on your diffractometer you will only have
one set of instrument parameters that affect the whole powder pattern.
These instrument parameters are not refined if you are studying a sample.
You only refine them when you are calibrating  your instrument (usually
using a powder pattern collected on a standard sample obtained for that
purpose).

You may mean you need your sample to show different profile widths for
different phases. In that case (the usual analysis case) you can model
profiles widths using size and strain broadening parameters of each of the
phases (click on each phase and go to the 2nd tab "Data" where sample
contributions to peak shape/width are shown). The effect on peak profile
shape/width may be the same (ruled by the same general equations) but are
attributed to physical phenomena in the crystallites of your sample, not to
those in the instrument.

GSAS I used to have both instrumental and sample parameters in the same
equation (refining one parameter for the sum of instrument and sample
contributions), making it impossible to differentiate between both in the
final result unless you knwe one of the contributions in advance. GSAS II
takes a more reasonable approach. In both versions of GSAS the instrumental
parameters (that you should not refine in an normal analysis) are provided
in the instrument parameter file (*.prm, *.ins, *.inst) and they are kept
explicit in GSAS II, differently than in GSAS I.

In summary, you want to fit your data using sample-related phenomena, such
as microstrain or size broadening for each phase, not different instrument
parameters for both phases.

I hope this helped and happy new year!

Leopoldo
--
#CONCIENCIA6+1

Prof. Agr. Dr. Leopoldo Suescun
Cryssmat-Lab/DETEMA, Facultad de Química, Universidad de la República.
URL: http://cryssmat.fq.edu.uy/leopoldo/leo.htm
e-mail: leopoldo at fq.edu.uy
Tel: (+598) 29290705
Fax: (+598) 29241906*
Mailing address:
Cryssmat-Lab./DETEMA
Facultad de Quimica
Av. Gral. Flores 2124
Montevideo 11800
Uruguay

Seguime en/Follow me at ResearchGate
https://www.researchgate.net/profile/Leopoldo_Suescun

ORC*ID*: https://orcid.org/0000-0002-7606-8074



El vie, 30 dic 2022 a las 18:30, Emily Siska via GSAS-II (<
gsas-ii at aps.anl.gov>) escribió:

> Hello,
>
> I am analyzing data that requires separate refinement of peak profile
> parameters (or "Instrument parameters) for different phases...this is the
> default with GSAS I, but I do not see how to do it in GSASII.
>
> Is there a way to set up, in GSASII, to individually refinement instrument
> parameters for different phases?
>
> Thank you for your help.
>
> Best regards,
> Emily Siska
> _______________________________________________
> GSAS-II mailing list
> GSAS-II at aps.anl.gov
> https://mailman.aps.anl.gov/mailman/listinfo/gsas-ii
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.aps.anl.gov/pipermail/gsas-ii/attachments/20230101/39d1154c/attachment.html>