The structure and conductivity of new fluorite-type Bi 2O 3–Er 2O 3–PbO materials

Abstract

Fluorite-type fcc phases have been synthesised in the system Bi 2O 3–Er 2O 3–PbO by solid state reaction, and a partial air-quenchable domain of the fluorite-type phase has been established. Some of these materials display high oxide ion conductivities, notably (BiO 1.5) 0.80(ErO 1.5) 0.11(PbO) 0.09 and (BiO 1.5) 0.85(ErO 1.5) 0.12(PbO) 0.03, which have conductivities of 0.49 and 0.72 S cm − 1 at 750 °C, respectively, placing them among the most conductive Bi 2O 3-based materials. Conductivity was found to increase with increasing Pb 2+/Er 3+ ratio and decreasing (Er 3+ + Pb 2+)/Bi 3+ ratio. Positional disorder in the oxide ion sublattice was characterised by neutron powder diffraction. At room temperature, the oxide ion sublattice appeared to be completely disordered, with oxide ions only in 32 f and 48 i sites, and changes in occupancy with increasing Pb 2+/Er 3+ and (Er 3+ + Pb 2+)/Bi 3+ ratios were not significant. At 700 °C, there appeared to be oxide ions in 8 c sites for the material (BiO 1.5) 0.80(ErO 1.5) 0.11(PbO) 0.09, with a correspondingly smaller occupancy of the 32 f sites, whilst the occupancy of the 48 i sites had not changed significantly.