Structural stabilization of δ-phase Bi2O3 in the MgBi1.5RE0.5O4 system through rare earth substitution for improved ionic conductivity

Abstract

Fluorite-structured Bi(2)O(3)oxide materials are promising candidates for oxygen ion conductors. In this regard, we attempted to stabilise the delta-phase through rare earth ion substitution in a new series of compositions: MgBi1.5RE0.5O4(RE = Nd, Sm, Gd, Dy, Y). They exhibit a phase transformation from a rhombohedral (Nd-Gd) to a fluorite-type (Dy, Y) structure as the ionic radius of rare earth decreases. The electrical property studies show that conductivity is a function of crystalline structure and lattice volume. Maximum conductivity of 4.3 x 10(-2) S/cm is obtained for the Y composition at 1023 K. The conductivity of the rhombohedral composition decreases as the lattice volume decreases associated with the increased activation energy. Contrastingly, the conductivity decreases with the increase of the lattice volume from Y to Dy on account of delta-phase instability at higher temperature. These results demonstrate that structural stabilization of delta-phase Bi(2)O(3)can be achieved through Y substitution with more thermal stability.