title: Pressure-induced intermetallic valence transition in BiNiO3.
abstract: The valence state change of BiNiO3 perovskite under pressure has been investigated by a powder neutron diffraction study and electronic-state calculations. At ambient pressure, BiNiO3 has the unusual charge distribution Bi(3+)(0.5)Bi(5+)(0.5)Ni(2+)O3 with ordering of Bi(3+) and Bi(5+)charges on the A sites of a highly distorted perovskite structure. 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 Bi(3+)Ni(3+)O3. This unprecedented charge transfer between A and B site cations coupled to electronic instabilities at both sites leads to a variety of ground states, and it is predicted that a Ni-charge disproportionated state should also be observable.
authors.affiliation: Institute for Chemical Research, Kyoto University, Uji, Kyoto-fu 611-0011, Japan. masaki@scl.kyoto-u.ac.jp
authors.forename: Masaki
authors.initials: M
authors.lastname: Azuma
authors.forename: Sandra
authors.initials: S
authors.lastname: Carlsson
authors.forename: Jennifer
authors.initials: J
authors.lastname: Rodgers
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Tucker
authors.forename: Masahiko
authors.initials: M
authors.lastname: Tsujimoto
authors.forename: Shintaro
authors.initials: S
authors.lastname: Ishiwata
authors.forename: Seiji
authors.initials: S
authors.lastname: Isoda
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Shimakawa
authors.forename: Mikio
authors.initials: M
authors.lastname: Takano
authors.forename: J Paul
authors.initials: JP
authors.lastname: Attfield