XRD pattern is properly fitted by more than one space group of same crystal system in Le-bail fitting. How can we confirm its space group to perform Rietveld Refinement?
The final confirmation of the space group is made based on arrival at a convincing structure model upon Rietveld refinement. It is quite common from single crystal diffraction but even more from powder diffraction that the "systematic absences" allow different space groups. In principle you have to try them all upon structure solution. Some statistical measures can be used as hints for presence of a centre of inversion. Typically one would start with the highest symmetry and if you have good success there, this would typically be also the final solution.
Dear Rajnikant Upadhyay , in addition to Andreas Leineweber answer, you can also take advance of the material you are analyzing. Unless it has been synthesized by the first time, you can look for previous works where its space group was well defined. It could happen that your material has two or more polymorphs, but this could help to ease the process or the work involved in solving the structure.
Sometimes you can use an already described space group for your material, but the fitting is bad with your structure, which could point to a new polymorph.
Hope this helps. Good luck with your research.
Dear Manuel Gómez earlier my material has been reported in different space group(monoclinic) but in my case my pattern is properly fitted with Tetragonal space group in Le-bail fitting and also with more than one space group of tetragonal class.
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