[GSAS-II] crystal size broadening parameter

[Toby, Brian H.]

Hi Angeles, 

GSAS-II limits the size value to 10 microns. That size produces no observable broadening even with the highest resolution powder diffraction data. If your value refines to this limit, then your refinement is not showing size broadening with the instrument parameters you are using. 

If you are refining instrument parameters (U,V, W, X &/or Y) and the size parameter: don’t! You can only fit one set or the other. 

If you are not refining U,V, W, X &/or Y, how did you get these values? Are they reasonable? If they produce peaks that are too wide, then size will refine to be large (and microstrain small) to avoid adding even more broadening. 

If you have reasonable instrument parameters and are refining both size and microstrain, then this can be an indication that all sample broadening is in the form of microstrain and you should fix the size at any large value and not refine it. 

Brian

> On Feb 11, 2021, at 9:13 AM, M. Angeles Gomez de la Torre via GSAS-II <gsas-ii at aps.anl.gov> wrote:
> 
> Dear all,
> 
> I am using GSAS II to do quantitative phase analysis.
> 
> When refinining size, with isotopric domain size model and LGmix =1.0, sometimes in some phases the value converged to 10 and it is fixed.
> 
> What that this mean?
> 
> Thanks in advance
> 
> Angeles
> 
> -- 
> Dr. M. Ángeles Gómez de la Torre
> Profesora Titular de Universidad
> Dpt. Química Inorgánica, Cristalografía y Mineralogía
> Facultad de Ciencias, Universidad de Málaga
> Campus de Teatinos 29010 Málaga
> Telf: +34 952131877
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> Skype: angelesgt
> 
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