The structure and ionic conductivity of fluorite-related Bi20Ca7NbO39.5, Bi10.75Ca4.375GaO22 and the high temperature form of Bi9ReO17, formed by quenching from 800C, were studied by neutron powder diffraction, X-ray powder diffraction and impedance spectroscopy. All materials formed distorted δ-Bi2O3–related monoclinic superstructures of a fluorite-related hexagonal sub-cell. The super-cell, with P21/m symmetry, was derived from the cubic fluorite sub-cell axes (af, bf, cf) using the transformation matrix: (-1, 1, 1; 0.5, 0.5, 0; 1, -1, 1). Both Bi20Ca7NbO39.5 and Bi10.75Ca4.375GaO22 were shown to display good oxide ion conductivity (2.52 x 10− 5S/cm and 1.02 x 10− 5S/cm at 673 K with activation energies of 1.12eV and 1.25eV, respectively); quenched Bi9ReO17 had enhanced oxide ion conductivity (1.44 x 10− 3S/cm at 673 K) with a lower activation energy of 0.76eV.

The Structure and Ionic Conductivity of the Fluorite-Related Isostructural Materials Bi20Ca7NbO39.5, Bi10.75Ca4.375GaO22 and Quenched Bi9ReO17. M.Thompson, C.Greaves: Solid State Ionics, 2010, 181[37-38], 1674-9