Re: Size

Armel Le Bail ( armel@fluo.univ-lemans.fr )
Fri, 06 Mar 1998 10:37:31 +0100

At 09:13 06/03/98 -0800, Keith R. wrote:
>Dear all - as things seem a little quiet at the moment, perhaps someone
>could explain how texture and 'grain' size could be correlated simply as
>an artefact of Rietveld refinements ; why should the M-D texture
>coefficient associated with refinements from different materials be
>correlated to grain size estimates (unless of course such a correlation
>exists in the material) ?

If you mean the March-Dollase preferred orientation parameter, it has
no reason to be correlated with grain size (if the size is below some
limit). However it is fully correlated with grain shape. Spherical shape,
whatever a size < 1-10 microns, should allow to avoid preferred
orientation. Anisotropic shape like needle or platelet shapes can be
dramatic. Now if you make a powder pattern with 10 grains of 5mm,
even if they are spherical, you will have spurious effects :-).

Armel Le Bail - Universite du Maine, Laboratoire des Fluorures,
CNRS ESA 6010, Av. O. Messiaen, 72085 Le Mans cedex 9, France
http://fluo.univ-lemans.fr:8001/
http://www.cybercable.tm.fr/~cristal/welcome.html