A Novel Diamagnetic Insulating Quadruple Perovskite Oxide YCu₃Rh₄O₁₂

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A novel oxide YCu₃Rh₄O₁₂ has been obtained using high-pressure and high-temperature conditions of 12 GPa and 1573 K. Electron diffraction and synchrotron X-ray powder diffraction data demonstrates that YCu₃Rh₄O₁₂ crystallizes in a cubic AA′₃B₄O₁₂-type quadruple perovskite structure. The valence state is estimated to be Y³⁺Cu³⁺₃Rh³⁺₄O₁₂ by X-ray absorption spectroscopy. The electric resistivity and magnetization data prove that YCu₃Rh₄O₁₂ is a diamagnetic insulator, which is expected from the electron configurations of Cu³⁺ (3d⁸, low spin, S = 0) and Rh³⁺ (4d⁶, low spin, S = 0) ions. The first-principle calculation displays the insulating band structure for YCu₃Rh₄O₁₂. The valence state transition from Ca²⁺Cu^2.8+₃Rh^3.4+₄O₁₂ to Y³⁺Cu³⁺₃Rh³⁺₄O₁₂ indicates that the doped electrons by the substitution of Y³⁺ for Ca²⁺ are not simply injected to Cu and/or Rh ions, realizing unusual charge redistributions consisting of the simultaneous Cu oxidation (Cu^2.8+ → Cu³⁺) and Rh reduction (Rh^3.4+ → Rh³⁺).