On mardi 26 juin 2007, May, Frank wrote:
> If the reason for their use is "historic and somewhat convenient, but their
> usual application is based on no theory whatsoever," why does their use
> continue?
Because they fit the data in most cases. People who will still use them are
those who do not care about the shape of the reflections, but only about the
integrated intensities (the structure factor).
If you are only interested in the structure (the atomic positions within
the unit cell) and not the microstructure (size, strain), UVW are generally
sufficient.
Fundamental parameters is (much) more correct but requires an accurate
description of the experiment - too much work if you won't interpret
the 'true' size broadening eventually.
> It is generally recognized that adding parameters to a least squares
> fitting process causes refinement to proceed to a lower residual
> (R-factor), even if the results are not physically meaningful. Would this
> not be the case when one adds U,V,W in Rietveld structure refinement?
3 parameters to model your profiles is not that much in order to model the
different effect of broadening (size strain instrument...).
Vincent
--
Vincent Favre-Nicolin
Université Joseph Fourier
http://v.favrenicolin.free.fr
ObjCryst & Fox : http://objcryst.sourceforge.net
