Mixed electronic-ionic conductivity of cobalt doped cerium gadolinium oxide

The effect of small amounts (<5 mol %) of cobalt oxide on the electrical pr operties of cerium oxide solid solutions has been evaluated. Ce0.8Gd0.2O2-x (CGO) powder with an average crystallite size of 20 nm served as a model s ubstance for the electrolyte material with a high oxygen ion conductivity a nd low electronic conductivity in its densified state. Doping the CGO powde r by transition metal oxides (MeO) with concentrations below 2 mol % did no t change the ionic conductivity nor the electrolytic domain boundary. After long sintering times (2 h) at temperatures above 900<degrees>C, MeO and Ce O2 form solid solutions. However, short sintering times or high dopant conc entrations lead to an electronic conducting grain boundary phase short circ uiting the ionic conductivity of the CGO grains. Choosing proper doping lev els, sintering time and temperature allows one to tailor mixed conducting o xides based on CGO. These materials have potential use as electrolytes and/ or anodes in solid oxide fuel cells and ion separation membranes.