During refinement of some of my XRD data using FullProf, the values u, v and w parameters are coming very high.. Moreover, they are not of same order.. So, I wanted to ask whether there is any limit of the values of these parameters..
Kindly response..
Basically, the UVW values should be refined only for calibration sample like NIST 660 (LaB6) and not refined for real sample. For real sample you should provide the derived values of UVW, while only X Y (strain, crystallite size) parameters should be refined (for profile NPR=7).
I can share UVW, but it will change with different diffractometers and configuration of slits/detectors.
U V W X Y
0.004391 -0.000389 0.009813 0.129552 0.110100
Concluding, if there is no possibility of making calibration measurement, try to refine only W with X, later add Y parameter. Keep U and V =0, at least at the beginning
General answer would be that some of the parameters, according to the formula, should not get negative values.. Other than that, Łukasz Gondek is right. Especially when you are interested in size and strain of your material, you should keep to this approach.
If peak fitting is proper then these values are ok. For more details see similar discussion:
https://www.researchgate.net/post/In_FullProf_XRD_Fitting_which_FWHM_parametersu_v_w_should_be_negative
For this, I would recommend the latest preprint article at link DOI: 10.13140/RG.2.2.27720.65287/3 or at link https://www.researchgate.net/publication/352830671
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