Oxygen Intake/Release Mechanism of Double-Perovskite Type BaYMn2O5+δ (0 ≤ δ ≤ 1)

The oxygen intake/release processes of double-perovskite type BaYMn2O5+δ (0 ≤ δ ≤ 1) were investigated from the viewpoints of crystal structure and reaction kinetics. The X-ray diffraction study on the partially oxidized/reduced BaYMn2O5+δ products has revealed a clear indication of successive phase changes among three distinct forms with δ ≈ 0, 0.5, and 1: the oxygen intake/release processes could proceed with nucleation followed by a growth of the generated phase. It has also appeared that the oxygen intake reaction is controlled by surface reaction at 348 ≤ T ≤ 403 °C, while the oxygen release process is surface-reaction-controlled at 425 ≤ T ≤ 550 °C and nucleation-process-controlled at 600 ≤ T ≤ 750 °C. The activation energy for the oxygen intake process at 348 ≤ T ≤ 403 °C is Ea = 0.27 eV and is much smaller than those reported for any other perovskite-type oxides indicative of great affinity to oxygen molecules.