I am refining a synchrotron XRD data of oxide ceramic using Rietveld method in GSAS. After refining cell, profile parameters chi2 is 1.2. If I refine the atomic positions now will they be reliable? I have a confusion there. How may I feel whether my refined atomic positions are right physicswise? If the position goes to any local mimimum chi2 will be lower but it may not be the right value. What is the way?
If any detail is required to understand the query, please ask the point.
Dear
Santanu Pathak
You can look at Wyckoff positions of the atoms. Like for atom A(0, 0.5, z) then only z can be refine-able.
Bond angle , Bond length as well as lattice parameter (xrd peak positions) depends on atomic positions. You can evaluate your refined bond angles and bond lengths. They should reasonable and should able to explain other properties like magnetic, optical thermal etc.
Dear Rana Hossain, Thank you for you valuable comment. But XRD peak position does not depend on atomic position. Only peak intensities, bond lengths, bond angles change due to atomic movement.
In general, the atomic positions of of low z elements refined from x-ray diffraction data has lower reliability than the high z elements. I agree with you that, the intensity of the X-ray diffraction peak is the one which is contributed by the atom positions along with certain other factors, like type of atom, occupancy, thermal vibartion, absorption and so on. In order to know whether your refined atom positions are really meaning ful, you may look in to the bond length and bond angle variations with respect to the physical properties which you are cconcerned. If that make sense you may procede with the atom positions what you got from the refinement. Also refining too many parameters without any meaning is not suggested, you may use minimum number of parameters to get a good quality fit. The chi square values may fall below 1 if the data quality is not good. what is important is, getting the parameters which is physically meaningful.
- Badges
- Science topic
- Similar topics
- Mathematics