Defect Chemistry of Pr Doped Ceria Thin Films Investigated by in Situ Optical and Impedance Measurements

While oxygen defect equilibrium in functional oxide thin films has a strong impact on device performance and longevity, few methods exist for evaluating it in situ . In this study, simultaneous in situ optical transmission and electrochemical impedance spectroscopy measurements are demonstrated as powerful and convenient means for this purpose, utilizing Pr x Ce 1– x O 2−δ (PCO) with multiple oxidation states for Pr (3+ and 4+) as a model system. The Pr 4+ color center optical absorptivity increased linearly with the Pr 4+ concentration, each independently derived from optical and chemical capacitance measurements, respectively, at elevated temperatures (550–700 °C) and under controlled pO 2 (10 –4 –1 atm), validating the use of optical absorption as a convenient means for monitoring defect concentrations and oxygen nonstoichiometry. The extracted extinction coefficient for Pr 4+ (ε Pr 4+ = 5.86 ± 0.12 × 10 –18 cm 2 with y -axis intercept of 927.5 ± 207.3 cm –1 ) can now be utilized to study defect equilibria of PCO, and by extension other relevant oxide films, by optical means alone. This enables defect characterization at reduced temperatures where other characterization techniques, for example, chemical capacitance, may not be feasible.