Oxygen content in transition-metal oxides can vary depending on the valence state of the transition-metal ions as seen in topotactic changes of perovskite-type oxides like SrFe2+O2 ↔ SrFe3+O2.5 ↔ SrFe4+O3. Understanding such oxygen incorporation and release behaviors in the oxides is very important not only from scientific viewpoints but also due to their potential applications. An important point for studying the oxides with unusually high valence cations is that the incorporation and the release of oxygen can occur at much lower temperatures than those with typical valence transition-metal ions. We here focus on oxygen-release behaviors in the two distinct structural compounds with identical chemical composition; one of the B-site-layer-ordered double perovskite Ca2FeMnO6 with Mn4+ and unusual high valence Fe4+, and the other of the simple perovskite Ca2(FeMn)O6 with the B-site-cation disorder. When the B-site-layer-ordered Ca2FeMnO6 is heated in air, oxygen is released only form the two-dimensional Fe-O layer in the perovskite structure at 330 °C and 415 °C, suggesting successive changes of Ca2Fe4+Mn4+O6 → Ca2Fe3.5+Mn4+O5.75 → Ca2Fe3+Mn4+O5.5. In the B-site-disordered Ca2(FeMn)O6, on the other hand, oxygen appears to be released at approximately 390 °C by a single change of Ca2(Fe4+Mn4+)O6 → Ca2(Fe3+Mn4+)O5.5. We will also show details of accompanying structural changes during the reduction and discuss the effect of the B-site ordering in the oxygen release behaviors.

Oxygen-release behaviors in B-site-layer-ordered/disordered perovskites Ca2FeMnO6 with unusually high valence Fe4+

2019 Spring National Meeting

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