Successive Charge Transitions of Unusually High‐Valence Fe^3.5+: Charge Disproportionation and Intermetallic Charge Transfer

Abstract

A perovskite-structure oxide containing unusually high-valence Fe was obtained by high-pressure synthesis. Instability of the Fe in Ca Bi FeO is relieved first by charge disproportionation at 250 K and then by intermetallic charge transfer between A-site Bi and B-site Fe at 200 K. These previously unobserved successive charge transitions are due to competing intermetallic and disproportionation charge instabilities. Both transitions change magnetic and structural properties significantly, indicating strong coupling of charge, spin, and lattice in the present system.

Charge and spin order in Ca0.5Bi0.5FeO3 : Idle spins and f

“…3 Neutron powder diffraction data collected as a function of temperature on cooling from 300 K to 5 K in 10 K steps showed the same structural transitions observed in previous synchrotron powder diffraction data. [15] Both structural transitions were accompanied by the appearance of additional reflections in the neutron powder diffraction data ( This magnetic structure is compatible with the 2:1 ratio of Fe 3+ :Fe 4.5+ and provides evidence that the Fe cations are charge ordered with two antiferromagnetically ordered Fe 3+ layers for every one paramagnetic Fe 4.5+ layer. An attempt was made to refine a nuclear cell of the same dimensions as the magnetic cell against the neutron powder diffraction data to determine oxygen displacements associated with charge ordering of Fe 3+ and Fe 4.5+ but the resulting refinement was not stable and did not result in an improvement of the fit to the data.…”

“…X-ray powder diffraction data confirmed the as-synthesised Ca0.5Bi0.5FeO3 sample was single phase and crystallizes in the Pnma structure previously reported. [15] Magnetization and resistivity data collected as a function of temperature show two anomalies consistent with successive CD and intermetallic CT transitions (Fig. 1).…”

“…FeO has recently been reported to contain unusually high-valent Fe 3.5+ and to undergo sequential charge transitions on cooling due to competing charge instabilities. [15] Magnetic and transport properties show significant anomalies associated with the charge transitions.…”

High Pressure Synthesis and Physical Properties of Sr_{0.5−<i>x</i>}Ca_<i>x</i>Bi_0.5FeO₃

“…Fe 3.5+ in Ca 0.5 Bi 0.5 FeO 3 has been found to undergo successive charge transitions. Ca 0.5 Bi 0.5 FeO 3 shows a CD transition (Fe 3.5+ → 1/3Fe 4.5+ + 2/3Fe 3+ ) at 250 K followed by an intermetallic CT transition (1/3Fe 4.5+ + 1/4Bi 3+ → 1/3Fe 3+ + 1/4Bi 5+ ) at 200 K 6) . Half of the Bi 3+ ions at the A-site act as counter cations for accepting charges from the Fe 4.5+ ions in the CT transition.…”

Transformation of Perovskite BaBiO3 into Layered BaBiO2.5 Crystals Featuring Unusual Chemical Bonding and Luminescence

“…Bismuth exists in innumerable functionalm aterials with various coordination environments, resulting in the appearance of an array of properties such as superconductivity, [1] oxide ionc onductivity, [2] ferroelectricity, [3] and so on. [4,5] Thef ormation of these materials seems to be intimately associated with the lone-pair stereoactivityo fB i 3 + ,w hich makes it polarizable, and with the diverse oxidations tates that Bi can exhibit. [6][7][8] Among Bi-containing oxides, perovskite BaBiO 3 ,i nw hich octahedral [BiO 6 ]b reathes out and in for Bi 3 + and Bi 5 + ,r espectively,h as long been investigated.…”