WHOLE-PATTERN FITTING IN ENERGY-DISPERSIVE POWDER DIFFRACTION

A new procedure of pattern decomposition in energy-dispersive powder diffraction is presented. The total observed pattern is taken as a sum of incoherent and coherent scattering. The incoherent part is calculated from theoretical cross sections for individual atoms, the coherent part is described as a sum of discrete Bragg peaks and acoustic- and optic-phonon thermal diffuse scattering (TDS) is calculated from the Debye and Einstein models, respectively. The total TDS is scaled to be the scattering missing from the Bragg reflections due to thermal motion. The model pattern is convoluted by the instrument function calculated from the diffraction geometry, and the pattern is fitted to the observed one by varying the integrated Bragg intensities and thermal motion parameters. The method is applied to patterns of Mg, Al and Ti powders, leading to an unambiguous and self-consistent division to the background and the pattern of Bragg reflections. As an application, the flux of continuous radiation from a W-anode X-ray tube is determined using theoretical integrated Bragg intensities.