December 2010

Cerium dioxide (CeO2) is characterized by mixed ionic and electronic conduction at elevated temperatures, thus ionic and electronic conduction occur in parallel. Ionic charge transport proceeds through double positively charged oxygen vacancies. Electronic charge transport is related to a polaronic jump process of electrons between Ceria ions. The figure shows typical impedance spectra of Ceria single crystals measured in air. The equivalent circuit corresponds to a parallel RC-circuit. R is attributed to the bulk transport and C reflects the geometric capacity of the sample. When temperature rises the semicircles become smaller, and the resistance decreases. Since charge transport is an activated process in ceria, it shows an exponential dependence from temperature. Applications for Ceria based materials are heterogeneous catalysis, sensors and SOFCs. Picture submitted by J.-P. Eufinger