Two-Step Suppression of Charge Disproportionation in CaCu3Fe4O12 under High Pressure

The electronic properties of a perovskite Fe4+ oxide, CaCu3Fe4O12, pressurized in a diamond anvil cell at pressures up to 50 GPa, were investigated by X-ray diffraction, electrical resistance measurements, X-ray absorption spectroscopy, and 57Fe Mössbauer spectroscopy. The first transformation from a charge-disproportionated (Fe3+ and Fe5+) semiconducting high-spin state to an approximately charge-uniform (Fe(4−δ)+ and Fe(4+δ)+) metallic high-spin state occurred at ∼15 GPa. This was followed by a second transformation to a completely charge-uniform (Fe4+) metallic low-spin state at ∼30 GPa. This is the first observation of pressure-induced two-step suppression of charge disproportionation in perovskite iron oxides.