It was shown in paragraph 6 of JAC 35 (2002) 338-346 that size-broadened profiles given by both lognormal and gamma distributions can be approximated by a weighted sum of Lorentz and Gauss functions for a broad range of distribution dispersions. Besides, round robins can sometimes be long adventures...
Davor > -----Original Message----- > From: Leonid Solovyov [mailto:[EMAIL PROTECTED] > Sent: Wednesday, April 13, 2005 12:11 AM > To: rietveld_l@ill.fr > Subject: Re: Size Strain in GSAS > > > 8. The simple modified TCH model ("triple-Voigt"), used in > most major > > Rietveld programs these days, is surprisingly flexible. It > works well > > for most of the samples ("super-Lorentzian" is an example when it > > fails, as well as many others, but this is less frequent that > > onewould expect) and gives some "numbers" for coherent domain size > > and strain. If we are lucky to know more about the sample (for > > instance, the information is available that a lognormal size > > distribution, certain type of dislocations, etc., is most likely to > > be prevalent for majority of grains in > > the sample), those "numbers" will let us calculate real numbers that > > relate to the real physical parameters (say, the first moment and > > dispersion of the size distribution, etc.) in many cases, as > > discussed here previously. > > Good conclusion, but before deriving real numbers that relate to the > real physical parameters one needs first to calibrate the > pseudo-Voigt-based calculation of those "numbers" (Dv and Da, or > <L_volume> and <L_area> in other notations)using at least simulated > profiles for VARIOUS dispersions. > I hope that the round robin on simulated data will be translated into > reality soon. > > Leonid > > > __________________________________________________ > Do You Yahoo!? > Tired of spam? Yahoo! Mail has the best spam protection around > http://mail.yahoo.com >
