Charge-order melting in charge-disproportionated perovskite CeCu3Fe4O12.

A novel quadruple perovskite oxide CeCu3Fe4O12 has been synthesized under high-pressure and high-temperature conditions of 15 GPa and 1473 K. (57)Fe Mössbauer spectroscopy displays a charge disproportionation transition of 4Fe(3.5+) → 3Fe(3+) + Fe(5+) below ∼270 K, whereas hard X-ray photoemission and soft X-ray absorption spectroscopy measurements confirm that the Ce and Cu valences are retained at approximately +4 and +2, respectively, over the entire temperature range measured.

Valence transitions in negative thermal expansion material SrCu₃Fe₄O₁₂.

The valence states of a negative thermal expansion material, SrCu3Fe4O12, are investigated by X-ray absorption and (57)Fe Mössbauer spectroscopy. Spectroscopic analyses reveal that the appropriate ionic model of this compound at room temperature is Sr(2+)Cu(~2.4+)3Fe(~3.

Control of bond-strain-induced electronic phase transitions in iron perovskites.

Unusual electronic phase transitions in the A-site ordered perovskites LnCu3Fe4O12 (Ln: trivalent lanthanide ion) are investigated. All LnCu3Fe4O12 compounds are in identical valence states of Ln(3+)Cu(2+)3Fe(3.75+)4O12 at high temperature.

Suppression of intersite charge transfer in charge-disproportionated perovskite YCu3Fe4O12.

A novel iron perovskite YCu3Fe4O12 was synthesized under high pressure and high temperature of 15 GPa and 1273 K. Synchrotron X-ray and electron diffraction measurements have demonstrated that this compound crystallizes in the cubic AA'3B4O12-type perovskite structure (space group Im3, No. 204) with a lattice constant of a = 7.