A new highly conducting fluorite phase in the bismuth–zirconium–niobate system

Structural and electrical investigations in the Bi3Nb1−xZrxO7−x/2 system have been carried out using X-ray powder diffraction and AC impedance spectroscopy. Several different fluorite phases are observed in the system. At low substitutions (0.0≤x≤0.40), a fluorite δ-Bi2O3-type phase is observed with a fully reproducible linear Arrhenius plot up to 800 °C. Above this composition range, a second fluorite phase (δ′-phase) is observed, which has a slightly larger unit cell volume than the δ-phase and shows high-temperature conductivity in the same order of magnitude as δ-Bi2O3. The increase in both high- and low-temperature ionic conductivity in the δ′-phase compared to the δ-phase cannot be attributed to the increase in vacancy concentration alone and suggests that the structure of the δ′-phase is better suited to higher O2− ion mobility.