Synthesis of Functional Oxides Using Cubic Anvil Press
—BiNiO₃ Exhibiting Inter-site Charge Transfer—

Abstract

  High-pressure synthesis is a powerful technique in searching for new materials. We have found a large number of functional oxides using this technique. BiNiO₃ is a distorted perovskite compound with unusual Bi_1/2³⁺Bi_1/2⁵⁺Ni²⁺O₃ valence state. High-pressure neutron diffraction measurements and bond valence sum calculations show that the pressure-induced melting of the charge disproportionated state leads to a simultaneous charge transfer from Ni to Bi, so that the high-pressure phase is metallic Bi³⁺Ni³⁺O₃. The same inter metallic charge transfer accompanied with 2.6% volume shrinkage is induced by heating Bi_0.95La_0.05NiO₃ at ambient pressure.