Structure of Na₂S-GeS₂ glasses studied by using neutron and X-ray diffraction and reverse Monte Carlo modeling

Neutron and X-ray diffraction measurements were performed to investigate the structure of Na₂S-GeS₂ glasses synthesized by mechanical alloying. The Ge-S coordination numbers calculated from the total correlation functions show that GeS₄ tetrahedra form the basic framework structure of Na₂S-GeS₂ glasses. In addition, a three-dimensional structural model of the (Na₂S)₅₀(GeS₂)₅₀ glass was obtained by using reverse Monte Carlo (RMC) simulation on neutron and X-ray diffraction data, and it was compared with the RMC model previously obtained for a (Li₂S)₅₀(GeS₂)₅₀ glass. The results show that the Ge-S framework structures in the two glasses are almost the same in the short and intermediate ranges; that is, the Ge-S framework structures are formed mainly by the connection of corner-sharing GeS₄ tetrahedra. Many of the Na ions are coordinated by four S atoms, which are non-bridging S atoms and/or bridging S atoms.