Phase stability, structure and electrical conductivity in the system Bi2ZrxV1−xO5.5−(x/2)−δ

The BIMEVOX system, Bi2ZrxV1−xO5.5−x/2, has been investigated using ac impedance spectroscopy and X-ray powder diffraction, in order to examine the effects of vacancy and dopant cation concentration on γ-phase stability and ionic conductivity. Four crystallographically distinct phases are observed at ambient temperature over the composition range 0.05≤x≤0.50. Below x=0.10, the orthorhombic α-phase is seen. Between x=0.10 and 0.16, the β-phase is stabilised. The stabilisation of orthorhombic α and β phases at lower compositions is typical for BIMEVOXes and results from an ordering of oxide ion vacancies. At x=0.19, the data were modelled on a tetragonal γ-phase cell, while at compositions where x≥0.22 a mixture of the tetragonal γ-phase and Bi8V2O17 is observed. The electrical conductivity is correlated with the stabilisation of the various polymorphs within the system. The observed γ-phase stabilisation region and the solid solution limit are discussed with respect to the defect structure.