A Qualitative Account for Anisotropic Broadening in Whole-Powder-Diffraction-Pattern Fitting by Second-Rank Tensors

Anisotropic line broadening in cell-constrained whole-powder-pattern fitting (including the Rietveld method) is proposed to be modelled qualitatively. The object is primarily to improve the fit, with the expectation of an increase in the feasibility of an ab initio structure determination in difficult cases. In a first simple approach, distances from an origin to ellipsoid surface are considered to represent the directionally dependent widths and shapes. Improvements in the profile refinements with a decrease of up to about 50% in the R factors may be obtained in cases unaffected by faulting. Experimental cases support the method and show the application limits.