Local- and Intermediate-range Partial Structure Study of As–Se Glasses

To investigate the relationship between the partial structures and the stiffness transition in As_xSe_1−x glasses, anomalous X-ray scattering (AXS) and X-ray and neutron diffraction (XRD and ND) experiments were carried out. For the AXS experiments, anomalous terms near the absorption edges were experimentally obtained instead of the theoretical values with large ambiguities. The results were analyzed by reverse Monte Carlo (RMC) modeling to obtain partial structure factors, S_ij(Q), partial pair distribution functions, g_ij(r), and three-dimensional atomic configurations. The S_ij(Q) and g_ij(r) functions gradually vary with x; however, an important change was observed in the intermediate-range element-selective atomic structures (the so-called hyper-ordered structures) near the stiffness transition composition. With decreasing x across the so-called intermediate phase compositions, a rapid decrease of the As–As wrong bonds is visualized. However, the other anomalies found in Ge–Se glasses are not clearly observed, such as a rapid decrease in pre-shoulder position in S_SeSe(Q), a rapid decrease in the number of edge-sharing connections, and an exclusion tendency of the connections between the As(Ge) atoms sharing two Se atoms, which may be related to the anisotropic pyramidal atomic configurations around the As atoms in the As–Se glasses in contrast to the isotropic tetrahedral ones around the Ge atoms in the Ge–Se glasses.