Synthesis and Properties of Monoclinic and Cubic Forms of the A-Site-Ordered (BiMn₃)Mn₄O₁₂ Perovskite

We have obtained two new A-site-ordered manganese perovskite oxides with the common chemical formula of (BiMn 3 )Mn 4 O 12±δ with regard to their metal composition. The two phases were prepared through high-pressure synthesis under identical conditions except for the oxygen-to-metal ratio in the precursor mixture. Accordingly, they were found to differ from each other in the oxygen content. The less-oxidized phase possesses a monoclinic crystal structure and shows two magnetic transitions, at 28 and 59 K, whereas the more-strongly-oxidized and hence denser phase with a cubic crystal structure lacks the higher-temperature transition. Thus, the present work has demonstrated an attractive but not-yet-utilized possibility to tailor the properties of (A′A′′ 3 )B 4 O 12±δ -type cation-ordered perovskite oxides by means of oxygen-content control.