I have problem with Rietveld refinement using GSAS_EXPGUI software. When I try a refinement diffraction pattern obtained from analysis of a known powder (as SiO2, CeO2) I have a big problem in relative intensities of the peaks. In fact, my peaks have a relative intensity different from the reference pattern. Also, after phase parameter refinement I don't see an improvement, and my chi square is very high (200-300). Where is my error? I prepared the powder milling with agate mortar, and after that I put the powder in a specimen holder filling the hole. If I try the same refinement process with a diffraction pattern coming from the network (as a tutorial or example pattern) I haven’t had problems and obtain good results.
There are several possible explanations. Do you find differences in the maximum or integrated intensity? If the problem is with maximum then it can be a microstructure effect. If it is a problem with the integrated intensity then try preparing the specimen again. It is unlikely but it might be a problem of texture.
My problem is in The maximum intensity. If I have a microstructure problem what I can do To solve It? Is It necessary a longer milling (I milled The powder only for a minute)? Or is It better To use a automatic milling system? Thanks for your help!
Have you refined the scale parameters?
Did you do the "zero of goniometer" before starting the analysys?
Maybe you're not refining de scale parameters, or are using a bad CIF file.
You can also try to use preferred orientation parameters that in some cases could help with intensity problems during structural refinements
Other possibility: change your step/size, the slits (depending of the angle your analysis start) e use a PRS like 0.3 mm. A lot of problems with intensity are correlated to the instrumental choice, besides the sample.
thanks a lot to everyone; preparing another time my sample with smaller slits I solved my problem and I obtained a good refinement result (chi square 12). Thanks!!!
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering
- Powders