Electronic structure of As2Te3-GeTe crystalline compounds

Pure LaGaO3 and the super ionic conductor La0.9Sr0.1Ga0.8Mg0.2O2.85 are structurally investigated by powder neutron diffraction at ambient temperature, 800, and 1000°C. At 25°C a distorted perovskite structure (orthorhombic, pure: Pnma, doped: Imma) is observed for both phases. The high temperature measurements result in a rhombohedral perovskite (R3c) for pure LaGaO3, whereas La0.9Sr0.1Ga0.8Mg0.2O2.85 exists in the cubic aristotype (Pm3m). The importance of neutron diffraction studies for the determination of the phase relationships in the La-Ga-Sr-Mg-O system is pointed out. From detailed analysis of the Debye-Waller factors including anharmonic contributions the diffusion pathways of the oxygen ions in La0.9Sr0.1Ga0.8Mg0.2O2.85 are obtained. The anions move near an arc of a circle above the edges of the vertex-shared GaO6-octahedra.