Could be a split Oeq shell.
Shelly
On Fri, Jun 11, 2010 at 5:19 AM, Andy Connelly
Hello all,
I've been following this mailing list for ages and have learnt a lot, thank you. Now I have a problem and am hoping someone can help.
I have some really nice sodium uranate (Na2U2O7) data from the NSLS (X23A2) that I collected (embarrassingly) a couple of years ago. I have been trying to fit it and have never managed to get a satisfactory fit even to the first shell.
From the literature there should be 2 uranyl oxygens and 6 equatorial oxygens. If I fit these paths I get an amp (S02) value of 0.32 and negative sigma squared values (ss). I have tried to add paths from the second shell to reduce this amp value but no success. I do not believe that this value is real but I cannot find any problem in the background or in the fit. I have found similar problems for lithium uranate and some glass samples, all of which should have similar uranium coordinations. I can bring ss into a more sensible value but amp is always very low. I have tried several different .cif files for different uranate or uranyl systems and they all give roughly the same result.
I have found similar problems with some data I collected at Daresbury on a different Na2U2O7 sample so I do not think it is the sample or the beamline. Does anyone have any thoughts why this might be so?
Any help or suggestions would be most appreciated.
Thank you all in advance,
Best regards
Andy Connelly
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