The structure of Bi3TaO7 was examined by X-ray and neutron powder diffraction. The structure was that of an ordered defect fluorite and was refined using a cubic δ-Bi2O3 type sub-cell model. A defect structure model was proposed with Ta5+ in predominantly a distorted octahedral geometry. These tantalate octahedra were 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.

Defect Structure and Electrical Conductivity in Bi3TaO7. I.Abrahams, F.Krok, M.Struzik, J.R.Dygas: Solid State Ionics, 2008, 179[21-26], 1013-7