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?:abstract
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A novel quadruple perovskite oxide CeCu3Co4O12 has been synthesized in high-pressure and high-temperature conditions of 12 GPa and 1273 K. Rietveld refinement of the synchrotron X-ray powder diffraction pattern reveals that this oxide crystallizes in a cubic quadruple perovskite structure with the 1:3-type ordering of Ce and Cu ions at the A-site. X-ray absorption spectroscopy analysis demonstrates the valence-state transitions in the ACu3Co4O12 series (A = Ca, Y, Ce) from Ca2+Cu3+3Co3.25+4O12 to Y3+Cu3+3Co3+4O12 to Ce4+Cu2.67+3Co3+4O12, where the electrons are doped in the order from B-site (Co3.25+ â Co3+) to A\'-site (Cu3+ â Cu2.67+). This electron-doping sequence is in stark contrast to the typical B-site electron doping for simple ABO3-type perovskite and quadruple perovskites CaCu3B4O12 (B = V, Cr, Mn), further differing from the monotonical A\'-site electron doping for Na1-xLaxMn3Ti4O12 and A\'- and B-site electron doping for AMn3V4O12 (A = Na, Ca, La). The differences in the electron-doping sequences are interpreted by rigid-band models, proposing a wide variety of electronic states for the complex transition-metal oxides containing the multiple valence-variable ions.
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