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Résumé |
Recent topics on ordered perovskite structure oxides are highlighted. We have prepared several new functional ordered perovskite oxides by using high-pressure synthesis and epitaxial thin film growth techniques.
The first topic concerns a new multiferroic compound Bi2NiMnO6, which was synthesized in both bulk and thin-film forms. The crystal structure of the material is a double perovskite, in which Ni2+ and Mn4+ ions are ordered in a rock-salt configuration. Bi3+ ions at the A-site cause a noncentrosymmetric structural distortion which allows a spontaneous ferroelectric polarization at room temperature. Ni2+–O–Mn4+ magnetic paths lead to ferromagnetism through the superexchange interaction according to the Kanamori-Goodenough rule. A coupling between the ferromagnetic and ferroelectric interactions appears to exist, but it is quite small.
The second topic is on intriguing physical properties of new A-site ordered perovskite structure oxides. High-pressure and high-temperature conditions stabilize the square-coordinated Jahn-Teller Cu2+ ions in the original 12-fold coordinated positions of the perovskite structure, producing ACu3B4O12. The special ordered arrangement of the square-coordinated CuO4 units that align perpendicular to each other sets a characteristic structural framework, and the presence of Cu2+ ions at the A site and Cu-B interactions play crucial roles for the diverse and intriguing physical properties.
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