Leandro Not sure what the purpose of your refinement is but if it's quantification then your results would probably be in error to a large extent.
The references given by Alan Hewat and Lubo Smrcok is probably a good starting point. Data quality and model errors typically mean that atomic positions should not be refined for clays; especially for Kaolinite. Also, use a common beq value for all sites or take them from literature. A gobal beq could then be superimposed using something like prm b 0 scale_pks = Exp(-b / D_spacing^2);. For quantification try spiking the sample with a standard to determine the amorphous content. It is possible to get the peak shapes without changing peak intensities; if you need assistance then contact me off the list. Cheers Alan -----Original Message----- From: Leandro Bravo [mailto:[EMAIL PROTECTED] Sent: Friday, 16 March 2007 9:15 AM To: rietveld_l@ill.fr Subject: Re: Problems using TOPAS R (Rietveld refinement) Ok, I´m starting to have sucess in the kaolinite refinement, the quantification is giving me reasonable values. I´m refining the thermal factors, all the atoms positions in the kaolinite, the lattice parameters and the cystallite size. Lattice parameters and crystallite size are giving me very good numbers, with very low errors (about 0,09). In the thermal factors, I realized that alll of them tend to 20, so after all refinements I put them to 20, and refine all over again. I don´t care that much for atoms positions, I´m only using them because refining only lattice, thermal and cry size wasn´t enough to make a good calculated pattern to compare with the measured one. In the calcite and dolomite I refine: lattice parameters, cry size and thermal factors. And use on both a preferred orientation correction (spherical harmonics 4 th order). The RWP is about 16. I´d to hear some opinions about this strategy of refinement, if you think that I can spare some refining cycles or even fix some values to reduce erros in the refinement. _________________________________________________________________ Descubra como mandar Torpedos SMS do seu Messenger para o celular dos seus amigos. http://mobile.msn.com/
