I'm trying to determine whether a PDF card indicates a normal versus inverse spinel structure. Is this possible to determine using only angle and intensity in a powder pattern? This is for a Ni-Co-O spinel. Both ions are expected in both the octahedral and tetrahedral sites. My understanding is that the structure factors for Ni and Co are similar enough that it makes normal methods difficult.
Using neutron diffraction one can distinguish much better Co ( 2.49 fm) from Ni (10.3 fm) and O (5.80 fm) because they have different scattering lengths (in paranthesis).
These are good suggestions. However, my samples are thin films and have far too small volumes for neutron diffraction or Mossbauer and probably SANS. I have done XPS on them. These materials can be high or low spin Co2+, Co3+, Ni2+, Ni3+, Ni4+ some in both octahedral and tetrahedral sites. XPS interpretation is quite difficult. I think XAS will only give me valence information, which could be complementary to the XPS..
Any other ideas?
You should Know that some of materials have same XRD patterns because of the nearly same electron populations and crystal structure. So, when you take XRD pattern and find that the pattern is the same of the other, I suggest you use ICP for elemental analysis to find the exact amounts of the elements and use XPS analysis to find the cation environment. You can use EPR to find that I there is an unpaired electron or not.
If you are looking for inversion symmetry or the lack of it, then powder diffraction will not distinguish between the two. You will have to use a single crystal for x-rays.
As also suggested in the other answers, with powder diffraction is not possible distinguish the inversioni of spinels with elements so similar for what concern the scattering factors. I think it is very difficult!!
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