High pressure synthesis, crystal structure and physical properties of a new Ni(II) perovskite BiNiO3

A new triclinic perovskite, BiNiO3, has been synthesized at a high pressure of 6 GPa in an oxidizing atmosphere. Structure refinements based on synchrotron X-ray powder diffraction and bond-valence calculations revealed a disproportionation of the Bi ions into Bi3+ and Bi5+, both being located in distorted oxygen octahedra. Because of the presence of Bi5+, the oxidation state of Ni was +2, rather than +3 as had been expected; BiNiO3 thus showed insulating behavior with localized spins of S = 1.