Dear all, I am working on the material of Y3Al5O12 with 0.1 of cerium doping. I have tried to use FullProf for the rietveld refinement but was having a hard time to reduce the Rwp and chi2 value. I do notice some of my parameters were over the standard value( e.g. Biso would range above 5 with the standard value less than 1 and same thing as the occupancy). I have attached my refinement parameters as above. My technique was refining one parameters for each try. May i know any tips for better refinement or anything i should be aware of? Thank you.
Dear Khai Shenn Lau ,
You will find some considerations at
https://www.researchgate.net/post/In_Rietveld_refinement_what_is_the_value_of_Rp_and_Rwp_for_an_excellent_fit.
Nevertheless, it is hard to see only by the figure. The XRD seems a result of an asymmetric effect over the peaks.
If it is the case, an in-depth inspection of the peaks description after fitting is necessary to use an axial divergent peak description, available in FullProf fitting program. It would help to overcome the inadequate description lowering the Rw values.
The effect may arise due to packing faults, interstitial substitution, even lattice distortions induced by the doping.
Best regards,
WNM
Dear Wagner Da Nova Mussel,
Thank you for your answer. I will look into your suggestion. However, i wish to get clarify on whether its advisable to manual change the Biso value? Example, if i run the refinement and obtained the Biso of 5.6 (standard from journals was 0.5), can i change the value to 0.6 and proceed with the other refinement parameters? Does it work this way?
Regards,
KS Lau
Dear Khai Shenn Lau ,
Following your example, if the achieved Biso is 5.6, the program has no success finding a reasonable solution based on the parameters already considered.
It is possible to fix the Biso equals to 0.6 as stated in the literature. However, the fitting must be started from the very beginning, with the original parameters. The overall lattice and other variables need to reflect the initial conditions, not those reflected by a Biso of 5.6.
This value only means that an obtained minimum chi2 solution was achieved with an enormous atom thermal dislocation, with no physical meaning et al.
Fix the Biso at 0.5 and start over with the initial literature parameters, or with the reference (model) you already used.
Best regards,
WNM
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