A QUALITATIVE ACCOUNT FOR ANISOTROPIC BROADENING IN WHOLE-POWDER-DIFFRACTION-PATTERN FITTING BY 2ND-RANK TENSORS

Anisotropic line broadening in cell-constrained whole-powder-pattern f itting (including the Rietveld method) is proposed to be modelled qual itatively. The object is primarily to improve the fit, with the expect ation of an increase in the feasibility of an ab initio structure dete rmination in difficult cases. In a first simple approach, distances fr om an origin to ellipsoid surface are considered to represent the dire ctionally dependent widths and shapes. Improvements in the profile ref inements with a decrease of up to about 50% in the R factors may be ob tained in cases unaffected by faulting. Experimental cases support the method and show the application limits.