Intermediate- and short-range order in phosphorus-selenium glasses

State-of-the-art neutron and x-ray diffraction measurements have been performed to provide a definitive picture of the intermediate-and short-range structures of PxSe1-x glasses spanning two glass regions, x=0.025-0.54 and 0.64-0.84. Liquid P4Se3 and amorphous red P and Se were also measured. Detailed information was obtained about the development with increasing phosphorous concentration of intermediate-range order on the length scale similar to 6 angstrom, based on the behavior of the first sharp diffraction peak. Attention is also paid to the feature in the structure factor at 7.5 angstrom(-1), identified in earlier numerical simulations, provides further evidence of the existence of molecular units. The real-space transforms yield a reliable statistical picture of the changing short-range order as x increases, using the information about types and concentrations of local structural units provided by previous NMR measurements to interpret the trends observed.