[GSAS-II] instrument parameters

[Arianna Lanza]

Dear all,

I am new to GSAS II and have no experience with old-GSAS, so forgive me for the basic level of the questions.

I don't fully understand the meaning of the parameters describing the instrumental profile.

·         What is Z? I could not find it in the old-GSAS manual.

·         How can I judge if the U V W X Y Z are reasonable?  (in case I don't have a reference profile from a standard) And how should a well behaved peak width plot look like?

·         I read that U W X Y are constrained to be >= 0, while V should be <= 0. However I have a not so badly-fitted plot where U refined to very negative, V to very positive, W is small and negative, X is positive and Y negative. So (i) those parameters have no constraint by default!Why not? Can I do it with equations?; (ii) even from my naïve understanding it looks like a nonsense. Most likely it is because I have broad peaks and the interplay between strain/size/etc and instrumental parameters converged to this artificial mess. Is it possible to deconvolute the instrument contribution from the sample contribution, in absence of a standard?

·         SH/L is one unique parameter as opposed to 2 separate parameters in old-GSAS, what is its meaning now, the units and/or reasonable range?

If you can help with even partial answers or point out useful sources of information, I will be grateful!

Kind regards,


Arianna




,_,.-'´¨´'-.,_,.-'´¨´'-.,_,.-'´¨´'-.,_,,.-'´¨´'-.,_,.-'´¨´'-.,_,

Arianna Lanza, PhD

Center for Nanotechnology Innovation at NEST
Istituto Italiano di Tecnologia
Piazza San Silvestro, 12, 56127, PISA, Italy


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