Structural and electrical investigations in the Bi3Nb1−xZrxO7−x/2 system were carried out using X-ray powder diffraction and AC impedance spectroscopy. Several different fluorite phases were observed in the system. At low substitutions (0.0 ≤ x ≤ 0.40), a fluorite δ-Bi2O3-type phase was observed with a fully reproducible linear Arrhenius plot up to 800C. Above this composition range, a second fluorite phase (δ′-phase) was observed, which had a slightly larger unit cell volume than the δ-phase and exhibited 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 suggested that the structure of the δ′-phase was better suited to higher O2− ion mobility.

A New Highly Conducting Fluorite Phase in the Bismuth Zirconium Niobate System. F.Krok, I.Abrahams, W.Wrobel, S.C.M.Chan, A.Kozanecka, T.Ossowski, J.R.Dygas: Solid State Ionics, 2004, 175[1-4], 335-9