High-pressure synthesis, electronic states, and structure–property relationships of perovskite oxides, ACu₃Fe₄O₁₂ (A: divalent alkaline earth or trivalent rare-earth ion)

抄録

Recent investigations on the quadruple perovskite series, ACu₃Fe₄O₁₂ (A = divalent alkaline-earth metal or trivalent rare-earth metal ion), have demonstrated anomalous electronic phase transformations such as charge disproportionation and charge transfer. These behaviors originate from the unusual high valence Fe⁴⁺ (or Fe^3.75+) ions that are dominated by ligand holes. In this review, various structural transformations and electronic properties in ACu₃Fe₄O₁₂ perovskites are shown. Furthermore, intriguing structure–property relationships of the A³⁺Cu₃Fe₄O₁₂ perovskites are presented. The local structural distortions on metal-oxygen bonds, which are represented as bond discrepancies and global instability indices, are closely related to the electronic phase transformations at low temperature generating a wide range of remarkable phenomena such as negative thermal expansion, ferromagnetism, and metal–nonmetal transitions.