Ionic conductivity of highly defective oxides

Abstract

A simple explanation accounts for the general shape of conductivity versus defect concentration observed in highly defective oxide solid solutions (e.g. ThO₂ and ZrO₂ with CaO and YO_1.5). An oxygen vacancy VO will be bound or strongly impeded in its diffusion if it has one or more defect cations as neighbours. Strong vacancy repulsion also leads to the exclusion of certain configurations. The probabilities of such configurations computed in an independent site statistical approximation lead to effective carrier concentrations peaking at 13% for the MO₂-M'O system and at 16% for the MO₂-M"O_1.5 system in agreement with experiment. A number of refinements are discussed.