Dynamics and Thermochemistry of Oxygen Uptake by a Mixed Ce–Pr Oxide

The dynamics of oxygen uptake by mixed Ce_0.55Pr_0.45O_2–x oxide is studied in a pulsed oxygen supply mode using in situ high-temperature heat flow differential scanning calorimetry. It is stated that the oxidation proceeds in two regimes: a fast one at the beginning of the oxidation process, and a slow one, which is controlled by the diffusion of oxygen through the bulk of the solid at the later stages of the process. Analysis of the shape of calorimetric profiles reveals some processes, accompanied by heat release, that occur in the sample in the absence of oxygen in the gas phase. These could be due to both the redistribution of consumed oxygen in the oxide lattice and the lattice relaxation associated with the transformation of phases with different arrangements of oxygen vacancies in them. The heat effect (which diminishes from ~60 to ~40 kJ/mol in the course of oxygen uptake) associated with the oxidation of the reduced form of mixed Ce–Pr oxide, corresponds to the oxidation of praseodymium ions from (3+) to (4+).