Redox characteristics variations in the cation-ordered perovskite oxides BaLnMn2O5+δ (Ln = Y, Gd, Nd, and La) and Ca2Al1−xGaxMnO5+δ (0 ≤ x ≤ 1)

Abstract

Two series of manganese-based oxygen storage materials, BaLnMn₂O_5+δ (Ln = Y, Gd, Nd, and La) and Ca₂Al_1−xGa_xMnO_5+δ (0 ≤ x ≤ 1), were synthesized and characterized to clarify cationic substitution effects on the oxygen intake/release behaviors of these materials. The thermogravimetric data revealed that the isovalent substitutions neighboring the active sites for oxygen intake/release are very effective. For BaLnMn₂O_5+δ, fully-reduced δ ≈ 0 products with larger Ln ions showed oxygen intake starting at lower temperatures in flowing O₂ gas, resulting in a systematic relationship between the onset temperature and the ionic radius of Ln³⁺. Furthermore, the δ vs. P(O₂) plots at 700 °C indicated a systematic trend: the larger the ionic size of Ln³⁺ is, the larger oxygen contents the Ln-products exhibit. For Ca₂Al_1−xGa_xMnO_5+δ, on the other hand, the temperature-induced oxygen intake/release characteristics appeared to be influenced by Ga-for-Al substitution, where the onset temperatures of oxygen release (upon heating) and oxygen intake (upon cooling) are decreased with the increasing Ga content (x).