(Invited) Zirconia Doped Ceria As a Mixed Ion and Electron Conductor

Abstract

Introduction of zirconia into ceria is known to increase the oxygen vacancy concentration in the host fluorite, despite the fixed tetravalent state of zirconium. Here we use 4-probe conductivity and electrical conductivity relaxation (ECR) methods over a wide range of oxygen partial pressures and several temperatures to explore the implications of this behavior on the transport of ionic and electronic species as a function of Zr content, up to ~ 45 mol %. All materials studied display predominantly n-type electronic conductivity, with a strongly increasing electronic conductivity with increasing Zr content. The ionic conductivity also increases with Zr concentration, but only moderately, and accordingly, the electronic transference number increases. Despite higher electronic and ionic conductivities, the bulk chemical diffusion of oxygen in ceria-zirconia is comparable to that in ceria. Furthermore, the surface reaction constant is dramatically decreased upon Zr doping. The connections between these and related observations are discussed.