Variable temperature neutron diffraction study of Bi3ReO8 oxide ion conductor

Abstract: The crystal structure of fluorite-related Bi3ReO8 containing isolated ReO4 tetrahedra has been studied by powder X-ray and neutron diffraction at elevated temperatures. The phase is cubic and undergoes a phase transition between T ~150°C and 250°C passing from space group P213 at 25°C to I213 at higher temperature. The material is an oxide ion conductor and presents a sharp increase in conductivity at T ~450°C, with σ ~8×10−3 Scm−1 above 500°C. Two different long range oxide ion diffusion mechanisms involving vacancy and interstitial defects are proposed. Rotation of isolated ReO4 tetrahedra seem to facilitate the oxide ion conduction. [Copyright &y& Elsevier]