Electrical and Structural Characterization of BaMoNbO: The Relationship between Mixed Coordination, Polyhedral Distortion and the Ionic Conductivity of BaMoNbO.

The electrical and structural properties of the series BaMoNbO (x = 0.0, 0.1, 0.2, 0.3) have been determined. BaMoNbO crystallizes in a hybrid of the 9R hexagonal perovskite and palmierite structures, in which (Mo/Nb)O and (Mo/Nb)O units coexist within the structure. Nb substitutes preferentially at the octahedral site so that the ratio of (Mo/Nb)O tetrahedra to (Mo/Nb)O octahedra decreases with increasing x resulting in a reduction in the magnitude of the ionic conductivity from 1.3 × 10 S cm for x = 0.0 to 1.1 × 10 S cm for x = 0.3 at 300 °C. However, upon heating the conductivities of the solid solution converge, which suggests that the unusual thermal structural rearrangement previously reported for BaMoNbO preserves the high temperature conductivity. The results demonstrate that the presence of (Mo/Nb)O tetrahedra with nonbridging apical oxygen atoms is an important prerequisite for the ionic conduction observed in the BaMoNbO system.