Structure and Dynamical Properties of Superionic Conductors

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1. The cubic system of the space group denoted by O^5_-Fm3m with the lattice constant of alpha=5.833<plus-minus>0.003 A has been found feasible for the crystal structure of superionic phase of Cu_2Se at 473 K using the usual powder X-ray diffraction method. The conclusion has also been supported by the anomalous X-ray scattering measurement.2. The crystal structure of CuBrSe_3 at room temperature has been analyzed by the Rietveld method with X-ray powder diffraction data. It belongs to the orthorhombic system with the space group Pnc2. The structure of CuBrSe_3 includes the ordered arrangement of Cu^+ ions.3. Specific heat vs temperature curve was measured in the temperature range between 100 K and 523 K. New phase transitions in CuBrTe, CuITe and CulTe_2 were observed at 230 K, 281 K and 286 K, respectively. The new phases obtained by the present specific heat measurement at low temperature would be related to an ordered distribution of copper atoms.4. Phase diagram of CuBrTe-CuXTe (X=C1 and I) system was determined from the analysis of the specific heat vs temperature curves.5. Neutron inelastic scatterings of Cu_2Se, CuI, Cu_<1.8>Se and Cu_<1.8>S were measured by the time-of-flight method at room temperature. Low-lying despersionless excitations near *omega - 3.4 meV, which would be common to copper ion conductors, existed in these substances.