Rietan: a Software Package for the Rietveld Analysis and Simulation of X-ray and Neutron Diffraction Patterns

The Rietveld method of structure refinement with powder diffraction patterns was originally devised for the analysis of fixed-wavelength (angle-dispersive) neuron data [1] [2] but now constitutes a major breakthrough for the usefulness of X-ray powder data [3]. This powerful method has greatly extended the amount of structural detail which can be obtained routinely from powder diffraction patterns. It is applied to the investigation of crystal structures when single crystals cannot be prepared at all or when the properties of interest of the single-crystal form differ from those of the polycrystalline form, for example, in catalysts, sensors, and bioceramics. However, several problems limit the straightforward application of the method: restricted information contained in powder diffraction patterns, difficulty in correction of preferred orientation, inadequacy of profile shape functions so far used, flat and local minima, narrow convergence range, and inaccurate standard deviations [4]. A computer program, XPD, for the Rietveld analysis of X-ray powder data [5] has been extensively modified to overcome these difficulties to a considerable extent and to permit the refinement with neutron powder data as well [6]. This new version, called RIETAN (RIETveld ANalysis), plus XPD are distributed to more than 60 research groups, domestic and foreign. It incorporates almost all convenient features of a standard program coded by Wiles and Young [7], for example, handling of anisotropic thermal parameters and the two wavelengths in the Kα doublet, single-pass operation, multiphase capability, refinement.of lattice and preferred-orientation parameters, and R factors in various shells. In the description that follows, emphasis is therefore placed on features that are not implemented in their program.