Dear Alice,
The Gaussian component may be related to either the instrumental broadening or
a narrow crystal size distribution. In the case you described I see two
possible options:
1) You don’t properly take into account the instrumental contribution which is
most pronounced for big crystallites.
2) For your samples the size distribution of big crystallites is narrower and
you have to include the Gaussian component.
Best regards,
Leonid
*******************************************************
Leonid A. Solovyov
Institute of Chemistry and Chemical Technology
660049, K. Marx 42, Krasnoyarsk, Russia
www.icct.ru/eng/content/persons/Sol_LA
sites.google.com/site/solovyovleonid
*******************************************************
--- On Fri, 2/19/10, Alice Courleux <alice.courl...@univ-lyon1.fr> wrote:
> From: Alice Courleux <alice.courl...@univ-lyon1.fr>
> Subject: Microstructural analysis by fullprof
> To: rietveld_l@ill.fr
> Date: Friday, February 19, 2010, 1:34 PM
> Dear Rietvelders,
>
> I am using Fullprof to microstructural analysis of
> particles. I have one type of particle but different sample
> with different sizes (particles increase after heat
> treatment). Their crystallites size fluctuates between 10nm
> and 1µm. I know that 1µm is big for a refinement Rietveld.
> To calculate the size, I refine Y (Lorentzian componant)
> then Ig (Gauss component).
> If the crystallites are small (<20nm) I can only refine
> the Y parameter. If I try to refine Ig, I have a error
> message "negative Gaussian parameter" and no crystallites
> size.
> For bigger crystallites, I can refine Y and Ig. If I only
> refine Y, the crystallite size is smaller than the size with
> Y and Ig refinement.
> For the biggest crystallites if I only refine Y parameter
> the size is "99999nm". However if I refine Ig parameter too,
> I succeed to have a size (1300nm for example)...
> I don't understand why I can't refine Ig whatever the
> crystallites size... Is ther any reason to that?
> Should I only refine Y for all my samples? Or refine Y and
> Ig when it's work and only Y when Ig bugs?
> Have you ever seen this problem?
>
> Thanks a lot for your help.
>
> Best regards,
>
> Alice
>
> -- Laboratoire des Multimatériaux et Interfaces - CNRS UMR
> 5615
> Université Claude Bernard Lyon 1
> 3ème étage - Bâtiment Berthollet
> 43, boulevard du 11 Novembre 1918
> 69622 VILLEURBANNE Cedex
>
> Mail: alice.courl...@univ-lyon1.fr
> Tél: 04.72.43.12.34
>
>
>
