Defect structure and electrical conductivity in Bi3TaO7

The structure of Bi3TaO7 has been examined by X-ray and neutron powder diffraction. The structure is that of an ordered defect fluorite and has been refined using a cubic δ-Bi2O3 type subcell model. A defect structure model is proposed with Ta5+ in predominantly a distorted octahedral geometry. These tantalate octahedra are thought to form corner sharing chains in a similar way to that proposed in the isostructural phase Bi3NbO7. The thermal variation of conductivity and lattice parameter appear to be correlated with subtle changes in the oxide ion distribution.