On the intensity distribution within Debye-Scherrer rings. What is different in high pressure experiments? Part I: Theory

摘要

Generally, high pressure powder diffraction using diamond anvil cells (DAC's)fails to produce intensity data in the traditional powder diffraction sense as a result of ex-perimental constraints. This often makes the raw data unsuited for standard Rietveld refine-ments. In a study based on data collected using image plates at state of the art beamlines theintensity distribution has been closely scrutinized. It was found not to follow the crystal-lographically well known i.e. Poisson, gamma, normal or lognormal distributions. The inten-sities are far better described by the Pareto distribution originally developed for economicalstatistics. This distribution model is reconcilable with the experimental features of high pres-sure powder diffraction. An advantageous aspect of this distribution is the ability to extractmeaningful normally distributed intensities, which present a sound basis for least squaresminimization within structural refinement.