Re: indexing problem

[pstephens]

Topas software is very good at solving such short axis problems.  The advantage is that it will look at all of the peaks you feed it, instead of using just the first twenty or so to generate candidate solutions (the way that ITO and TREOR work).

If you don't have access to Topas, I suggest the following, which has been quite successful for me in the past.  Use the two axes you have to completely index the zone that contains the first reflections, and run a profile (Le Bail) fit using, e.g., fullprof.  Put in a dummy b axis of 1 angstrom, so it doesn't generate any reflection markers in the range of your data.  Refine the lattice parameters, so you get a clear indication of which peaks belong to your first zone and which do not.  The next step is to pray that your sample is monoclinic, so you can leave alpha and gamma = 90, and you only have to determine the lattice parameter b.  The first peak not indexed by your zone is probably the (010), (110), (011), (111), or (-111), and you can quickly calculate what the b parameter would have to be to fit each of those cases.  Type it in, run another profile, and see which one works best.  If that doesn't work, and you think your material is triclinic, it is still possible, but you have to identify three (h 1 ell) peaks and suggest indexations for them.  That needs at least half a dozen good peaks outside of the first zone, and a little computer program to search the candidates.  I don't know of any public domain software for that, but it's a good project to give a student to help them learn about reciprocal space geometry.

Good luck,
Peter

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Peter W. Stephens, Professor
Department of Physics & Astronomy
State University of New York
Stony Brook, NY 11794-3800