Dear Edouard,
You can try to refine the X parameter that follows U,V,W (FWHM
parameters) in the input file for FULLPROF. This will give you another degree
of freedom, in the sense that the eta parameter can now increase with 2theta
through the equation
eta = eta0 + X * 2theta
I hope this help you !
Best regards,
Claudio.
****************************************************
Claudio A. Perottoni
Universidade Federal do Rio Grande do Sul
Instituto de Fisica - Laboratorio de Altas Pressoes
Av. Bento Goncalves, 9500
CAIXA POSTAL 15051
91501-970 PORTO ALEGRE - RS
BRAZIL
PHONE:55-51-316-6500
FAX :55-51-319-1762
http://www.if.ufrgs.br/~perott/index.html
****************************************************
On Fri, 19 Nov 1999, you wrote:
>
> Dear Rietveld-mailing list users,
> As I just subscribed this e-list, let me present myself:
> My name is Edouard RENY, and I'm a fresh doctor is material Science
> (I obtained my Doctor degree in France this february). Now I'm a post-doc
> in Japan working on silicon clathrate structures.
> the Rietveld refinement program I use is Fullprof (with a DBWD viewer),
> And I have a problem in refining the X-ray peak profiles of one of my samples:
> Whatever I do, the refinement leads always to Gaussian type profiles
> which we can see on the .prf file, at high 2 teta, don't match at all with
> the experimental profile. This sample contains some silicon, and there, no
> problem to refine the
> peak profiles (even if intensities are not perfect). However at low two
> tetas (for 2tetas < 50deg) ,
> calculated peak shapes match quite well with experimental data.
> (see fig1.gif. At higher 2tetas, it's even worse)
> I use a PseudoVoigt, it leads usually to eta=0.35 (mixing parameter)
> approximatively.
> If I fix it to more lorentzienne values (0.6 or 0.8 for instance),
> residuals become too high.
> U,V, W combination refining converges but if we free eta,
> I always finish by having Gaussians peaks mixing the Ka1 and Ka2
> contributions as one peak.
> What is strange is that there is no problem for the impurity silicon phase
> (peak shapes are
> well defined). The profile parameters of the two phases are not commonly
> refined.
> Has anyone been through this problem? has anyone have an idea of refinement
> procedures which would lead to a better peak profile refinement and avoid
> this false minimum
> where the program always seem to converge?
> Thanks in advance for your help
> Sincerely
> Edouard RENY
>
