Stephen's broadening model (implemented in full prof software) takes care of broadening observed in certain x ray diffraction peaks of a diffraction pattern by considering microscopic strain in the material. HKL indices are assigned to S factors obtained from this model. How these HKL indices are correlated with Miller indices (h,k,l)? It is true that Stephen's model is phenomenological, but is it possible to give physical interpretation of these S factors?
Some information on this issue can be found here
Understanding anisotropic microstrain broadening in Rietveld refinement
- Zeitschrift für Kristallographie 226(12):905-923
- DOI: 10.1524/zkri.2011.1413
For rhombohedral system in hexagonal setting four S factors S400, S004, S112, and S301 will allowed according to stephen's model, but full prof is giving out only three S factors ( S400, S004, S112). What could be the possible reason for this?
Fullprof does not have S202 refined? I have to check the equations, but maybe the information is contained in S112. This is the number of independent paramameters also available for Laue group 6/mmm. Hence it appears that Juan Rodriguez-Carvajal has decided to enforce a higher symmetry for the line broadening. You may try to check which parameters are refined in the case of a LeBail fit with P6/mmm symmetry and (always the first step) whether the Fullprof manual provides the expressions for the different Laue classes. Note that there are different choices of the indepdent parameters possible.
@ Andreas Leinweber
Maybe there is some confusion or I am missing something. For R-3m space group in hexagonal setting we will take hkl planes and lattice parameters using rhombohedral to hexagonal transformations, but we will still take the point group -3m (which is symmetry of the system). For -3m, we have S400, S004, S112 and S301 terms. S202 will be equivalent to S112. Please let me know whether I am missing some point. I have not considered 6/mmmm symmetry.
The parameters refer to the hkl. So dependending on the choice of the unit cell, the S_HKL parameter will change. Of course the number of independent parameters remains the same. But the interrelationships between the paramaters may be complex. Therefore, you may have different refined parameters if you have a rhombohedral structure with primitive or hexagonal setting. E.g. in the case of primitive rhobohedral S400 = S040 = S004. The indepdent parameters turn up somewhere else.
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