Tuning the Pr Valence State To Design High Oxygen Mobility, Redox and Transport Properties in the CeO2–ZrO2–PrOx Phase Diagram

The preparation and characterization of pure fluorite-type phases allowed exploring the CeO2–ZrO2–PrOx (CZP) phase diagram. On the basis of magnetic susceptibility measurements, the Pr4+/Pr3+ molar ratio of several oxides annealed at T = 700 °C under air was determined; the higher the Zr content, the lower the Pr4+ concentration. Thermogravimetric analysis and temperature-programmed reduction measurements showed various Pr and Ce reduction steps. The Pr4+ reduction starts at T = 250 °C and is maximum around T = 400 °C. For the most reducible compositions, which exhibit the lowest Zr content and the highest Pr rate, the reduction phenomena strongly depend on the Pr/Ce molar ratio. As a remarkable result, Pr and Ce reductions can simultaneously take place at lower temperature (T > 430 °C) than for oxides of the CeO2–ZrO2 solid solution evidencing that the increase of Pr content also allows enhancing the reducibility of Ce4+ at low temperature. On the basis of a discussion taking into account the probability...