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Date: Wed, 24 Feb 1999 11:19:59 +0100
To: RIETVELD_L Distribution List <[EMAIL PROTECTED]>
From: Armel Le Bail <[EMAIL PROTECTED]>
Subject: Re: rietveld Software for powders containing amorphous
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Dr Hervé Brequel wrote :
>If anybody knows something about Rietveld method and
>amorphous compounds, please tell me
Hints and tips about this controversial approach of amorphous
materials are found at :
http://pcb4122.univ-lemans.fr/aritve.html
Controversial because of the need to consider mean small
models deriving from crystalline structures, the disorder
being simulated by microstrain and size effects which broaden
the "reflections".
Anyway, it was recently shown that the RDM (Rietveld for
Disordered Materials) and RMC (Reverse Monte Carlo) methods
could be reconciled. A small RDM satisfying model, enlarged
by multiplying the "cell" parameters by 2, 3 or more, can
become a succesfull RMC model, keeping strict constraints
on coordinations in case of framework glasses. See :
http://pcb4122.univ-lemans.fr/glasses/versailles/poster.html
http://pcb4122.univ-lemans.fr/microstruct/denver/t16.gif
http://pcb4122.univ-lemans.fr/glasses/albpaper.html
Luca Lutterotti approach of amorphous silica is based
on the best RDM model as published in J. Non-Cryst. Solids,
183, 1995, 39-42.
Best wishes,
Armel Le Bail - Universite du Maine, Laboratoire des Fluorures,
CNRS ESA 6010, Av. O. Messiaen, 72085 Le Mans Cedex 9, France
http://www.cristal.org/
