I am just starting out with rietveld refinement. I have been trying to get a good fit for my data of the compounds Bi0.8La0.2Fe(1-x)Zrx using the software Fullprof. But in all my 4 compositions (x=0,0.02,0.05 and 0.1) there seem to be some intensity mismatch of the structural model and observed data. I am attaching the pcr file for the composition Bi0.8La0.2Fe0.98Zr0.02 and also the starting structural model. A picture showing the fit of the data is also attached. As can be seen, the peaks around 2theta = 22, 46 etc. show positive deviation (calculated value is higher) while some peaks have lower calculated value. My obtained chi^2=9.2. How can I improve the fitting ? I am thinking preferred orientation is not the cause since the same trend is seen in all four of my samples.
Hi Usama,
There are a lot of factors that can influence this mismatch between observed and calculated peaks, from preferential orientation of your crystallites to structure of your sample that could be different by the one that you're trying to model.
I would suggest you to collect data counting for a longer time. Also trying to improve the resolution (changing the slits of your diffractometer) could help you to elucidate if you have phases with similar cells coexisting or even if you have a change in the crystal system (e.g. from orthorhombic to monoclinic).
You can also use "free format" for the experimental data. examples: https://www.ill.eu/sites/fullprof/php/tutorials.html
I hope this helps. Goodluck!
Thanks for the answer Galib. Recollection of data is not possible at present time. And yes the spacegroup could be something other than the one im using. But for now this is the best matching spacegroup I have. I would like to know if there is anything Im overlooking that could help me fit the data without changing the entire spacegroup !
Actually, the fit you show in your picture is quite good. Given inherent noise and other issues such as particle size of actual material, I honestly doubt you would get a better fit.
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