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

Abstract

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 ${\mathrm{P}}_{x}{\mathrm{Se}}_{1\ensuremath{-}x}$ glasses spanning two glass regions, $x$ $=$ 0.025--0.54 and 0.64--0.84. Liquid ${\mathrm{P}}_{4}$Se${}_{3}$ 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 \ensuremath{\sim}6 \AA{}, based on the behavior of the first sharp diffraction peak. Attention is also paid to the feature in the structure factor at 7.5 \AA{}${}^{\ensuremath{-}1}$, 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.