Dear colleagues,
Does anyone have experience with refining diffraction data (2theta, CuKalpha) that exhibit super strong peak asymmetry due to the absence of Soller slits in the instrument? I am trying to fit such data, but the standard asymmetry parameters seem insufficient.
I’m using FullProf with npr=7 and have tried adjusting S_L, D_L, and Asy1–4, it helps a bit but these settings do not adequately capture the peak shapes.
Are there other programs or parameterizations that handle this kind of asymmetry better?
Thank you in advance!
Yeah, I assume you are using the Fingerle-Cox peak description. I have not found it to give perfect results. I'm not surprised with no SS, the asymmetry to so pronounced at low angle that it's difficult to fit. I don't know FullProf's options, but if you can, try an asymmetric Pearson VII function with variable exponent. It may not be possible to fit well without custom software, as we almost always use SS, especially for low angle data, so most software will do a much better job when data was collected with both incident and diffracted beam SS. Sorry to not be more helpful.
The asymmetry will most likely be caused by the increased axial divergence present when the Soller slits have been removed. It should be fairly easy to analyse using a Fundamental Parameters approach to modelling instrument width - such a model is implemented in e.g. TOPAS.
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