Dera friends, I'm doing Rietveld refinements in TOPAS; I get rather good fit of the reflections, rather good wt.%, but I've observed large errors for the CrySize (Lorentzian) values for some introduced Structures. I've tried to change it by refining CrySize (Gaussian), but it only changed in few particular cases. I'm rather sure that the intrumental parameters (geometry of the diffractometer was analyzed with the use of LaB6, Si, and other standards) and corrections (sample displ. etc.) are OK and I suppose these factors shouldn't influence (?) the CrySize values. I always constrain the minimum (20 starting value) and maximum (10000 nm) value for CrySize; I usually refine strain, but I've noticed that it doesn't influence the results (at least the wt.% calculated). Rwp, goodness of fit and Durbin-Watson statistics R values are OK; also, the calculated background line is "flat", i.e., there is no mistaking of the background with reflections; the shapes of the reflections in the calculated diffractograms seem to be OK, too. I was thus wondering if these high errors coming from the CrySize are that important for the refinement?
Best regards, -- Łukasz Kruszewski, Ph.D., adjunct Polish Academy of Sciences Institute of Geological Sciences Twarda 51/55 str. 00-818 Warsaw Poland
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