Praseodymium doped ceria: Model mixed ionic electronic conductor with coupled electrical, optical, mechanical and chemical properties

Praseodymium doped ceria, PrxCe1 − xO2 − δ (PCO), exhibits many interesting and unusual properties including a pO2 dependent ionic conductivity, an anomalously large thermal expansion coefficient in air, and a significant electronic conductivity component at elevated pO2. These unusual features are discussed in terms of the variable valent nature of Pr at elevated pO2, its position within the ceria band gap and the creation of an impurity band supporting small polaron transport. Implications for use of PCO as a ceria solid electrolyte compatible cathode, stress induced chemical expansion and optically detected redox kinetics are analyzed and discussed.