Structural Characterization of High Pressure Behavior of "Crystallographically Challenged" Materials Using PDF Analysis from X-ray Total Scattering

Evaluating atomic structure in glassy and nanocrystalline materials using traditional powder diffraction analysis techniques (e.g., Rietveld method) is often hindered by the broadening of diffraction maxima resulting from the effects of particle size, disorder and lack of long range order. These effects are manifested as a significant diffuse scattering component in a diffraction pattern, which contains important information regarding the local atomic arrangement in the structure. Total scattering and pair distribution function (PDF) analysis is therefore a valuable tool for evaluating such materials because the diffuse scattering, as well as the Bragg component, are included in the analysis and therefore information regarding the short-, medium-, and long-range atomic ordering is attainable. We have recently used the PDF method to probe the atomic structures of a number of nano-sized or glassy metal chalcogenides and oxides at ambient and under high pressure conditions. Changes in structure are modeled and, in select cases, correlated with cahnges in physical properties.