Short- and medium-range order in Sb–Se glasses

Neutron diffraction measurements were performed to investigate the structure of Sb_xSe_100−x bulk glasses with x=5, 10, 15, 20 and 25 at% Sb. The total pair distribution functions show two peaks at 2.36 Å and 2.64 Å, which are attributed to Se–Se and Sb–Se bonds, respectively. The coordination numbers calculated from these peaks indicate that Sb atoms are three-coordinated and Se atoms are two-coordinated for all the above compositions. However, the composition dependences of the first two peaks in the structure factors show an obvious change between 15 and 20 at% Sb, indicating that the medium-range structure is changed in this range of Sb content. In order to elucidate the medium-range structure, reverse Monte Carlo simulation was used with coordination number constraints. The structure models consisting of a mixture of the SbSe_3/2 network and Se_n chain clusters were in good agreement with neutron diffraction data for Se-rich glass (5, 10 and 15 at% Sb). On the other hand, a better fit was obtained for Sb₂₅Se₇₅ glass with a model based on the network structure formed by connected SbSe₃ units. - Graphical abstract: A 50 Å slice of the RMC configuration for Sb₁₅Se₈₅ glass. - Highlights: • Sb atoms are three-coordinated and Se atoms are two-coordinated. • The medium-range structure changes between 15 and 20 at%. • The phase-separation tendency is observed in Se-rich glasses.