Enhancement of ionic conductivity by dispersed oxide inclusions: influence of oxide isoelectric point and cation size

Abstract

Doping of a halide salt by dispersion of oxide particles rather than subtitutional impurities is a proven method of enhancing the extrinsic ionic conductivity of the host. The conductivity mechanism in any space-charge layer at the oxide/host interface is determined by the chemical reactions at the interface. These interactions are discussed by analogy with the particle hydrates. The enhancement of the F^--ion conductivity in PbF₂ is predicted to be via F^--ion vacancies in the space-charge region and to increase with decreasing oxide isoelectric point and increasing normal anion coordination of the oxide cation. This prediction accounts satisfactorily for the relative enhancement factors measured for PbF₂ containing dispersed CeO₂, SiO₂, ZrO₂ and Al₂O₃.