I am trying to do Rietveld analysis but the d-spacing are not matching for Cr2O3 by calculation with the observed values. I put alpha=90 degrees in d-spacing formula for rhomboderal but not getting the results. I could not even match JCPDS values by putting 90 degrees alpha value. Please guide me how to find angles alpha, beta and gamma for different crystal planes for Cr2O3
Hi Sudhanshu,
I guess you are mixing up hexagonal and rhombohedral settings of this structure.
Cr2O3 has a rhombohedral crystal structure and can be described with rhombohedral axes. Resulting also in rhombohedral h.k.l. indices for the diffraction peaks and rhombohedral formulae to calculate the peak positions from the unit cell dimensions.
It is however much more common to describe rhombohedral crystal structures with a hexagonal unit cell, resulting in different unit cell dimensions, h.k.l indices and formulae to calculate peak positions.
For Cr2O3 the unit cell dimensions are:
Rhombohedral setting: a = b = c = 5.35 Å; alpha = beta = gamma = 55.13 degrees.
Hexagonal setting: a = b = 4.95 Å; c = 13.57 Å; alpha = beta = 90 degrees, gamma = 120 degrees.
When you want to reproduce the JCPDS data you better use the hexagonal settings, just remember to use the formulae for the hexagonal system as well.
regards,
Harry
@ Harry J. Wondergem: Is it applicable for La0.6Sr0.4Fe0.8Co0.2O3 (rhombohedral structure) ?
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