Pressure-Induced Spin-State Transition in BiCoO₃

Abstract

The structural and electronic properties of BiCoO(3) under high pressure have been investigated. Synchrotron X-ray and neutron powder diffraction studies show that the structure changes from a polar PbTiO(3) type to a centrosymmetric GdFeO(3) type above 3 GPa with a large volume decrease of 13% at room temperature revealing a spin-state change. The first-order transition is accompanied by a drop of electrical resistivity. Structural results show that Co(3+) is present in the low spin state at high pressures, but X-ray emission spectra suggest that the intermediate spin state is present. The pressure-temperature phase diagram of BiCoO(3) has been constructed enabling the transition temperature at ambient pressure to be estimated as 800-900 K.

Prediction of variation in d-orbital occupancy in strain induced tetragonal phase of BiFeO3 thin film

“…26 Moreover, pressure induced structural and spin state phase transitions have also been found in other Co oxides such as BiCoO 3 and SrRu 0.5 Co 0.5 O 3 , etc. 27,28 More recently a pressure induced spin reorientation and spin state transition have been reported in SrCoO 3 . 19 Three spin states have also been reported on Fe sites in CuFeO 2 in rhombohedral and monoclinic phases.…”

A new cubic perovskite in PbGeO3 at high pressures

“…Many novel phase transitions in perovskite compounds have been thus discovered. For instance, the cubic PbCrO 3 perovskite (Phase I) transforms reversibly to another cubic perovskite (Phase II) with a 9.8% volume collapse at the pressure of ∼1.6 GPa (Xiao et al 2010); the multiferroic material of PbVO 3 , which crystallizes in the polarized tetragonal perovskite (P4mm) structure at ambient conditions, changes reversibly to a cubic perovskite with >10% volume collapse at about 2 GPa (Belik et al 2005); BiCoO 3 has the same polarized structure as PbVO 3 at ambient conditions but transforms to the orthorhombic perovskite (Pnma) with a 13% volume reduction at 3-4 GPa, which is induced by the high-spin to low-spin electronic transition in Co 3+ cation and the complete suppression of the polarized character in the Bi 3+ cation (Oka et al 2010). Silicate perovskites are the primary mineral components in the Earth's lower mantle (Kesson et al 1998;Wood 2000).…”

Magnetic Field Effects in a Correlated Electron System with Spin-State Degree of Freedom — Implications for an Excitonic Insulator —

“…The characteristic temperature dependences of the electrical resistivity and the magnetic susceptibility are interpreted as a crossover between the LS state of the (t 2g ) 6 configuration with S = 0 and the HS states of (t 2g ) 4 (e g ) 2 with S = 2. 2) Several exotic phenomena, such as the giant magnetoresistance, 10) magnetic clusters, 11,12) and a ferroelectricity, 14) are attributable to the spin-state change.Correlated electron materials with SSDF is recently reexamined as a plausible candidate of the excitonic insulator (EI). [15][16][17] The EI state has been studied since 1960s in the narrow gap semiconductors and semimetals, [18][19][20][21][22] and is recently reexamined from the modern viewpoints.…”