The influence of composition upon resultant mixed conductivity was analyzed for the fluorite-type compositions Zr0.1Ce0.7Pr0.2O2−δ, and Ce0.8Pr0.2O2−δ. Measurements of O concentration cell emf, combined with impedance spectroscopy at elevated temperatures revealed the materials to be predominantly ionic conductors in oxidizing conditions and to exhibit a decrease in both ionic and electronic conductivities with decreasing pO2. Ion transference numbers measured under these conditions showed a positive temperature dependence, with typical values t0 = 0.8 and 0.9, respectively, for the two compositions at 950C. The combination of this information with results of Coulombic titration, facilitates analysis of the pO2 dependence of total conductivity measured by a steady-state electrochemical technique between air and reducing conditions. In more oxidizing conditions, depletion of total conductivity with decreasing pO2 resulted predominantly from a decreasing ionic conductivity. This was one of first examples in the literature where a fluorite-type material was shown indisputably to exhibit such behavior. These materials showed significant levels of mixed conductivity in both reducing and oxidizing conditions. In more reducing conditions, an increase in total conductivity was related to increased n-type conductivity upon the reduction of cerium.

The Defect Chemistry of Ce(Pr,Zr)O2−δ. D.P.Fagg, J.R.Frade, V.V.Kharton, I.P.Marozau: Journal of Solid State Chemistry, 2006, 179[5], 1469-77