High-Pressure Synthesis and Magnetic States of Magnetoplumbite Cobaltates CaCoO and BaCoO.

Novel cobalt oxides, CaCoO and BaCoO, have been synthesized under high-pressure and high-temperature conditions of 7 GPa and 1373 K, respectively. Rietveld refinement using synchrotron X-ray diffraction data indicates that the CaCoO and BaCoO crystallize in a magnetoplumbite structure with a hexagonal space group of 6/ (No. 194) as well as SrCoO.

A Sequential Electron Doping for Quadruple Perovskite Oxides CuCoO ( = Ca, Y, Ce).

A novel quadruple perovskite oxide CeCuCoO 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 -site. X-ray absorption spectroscopy analysis demonstrates the valence-state transitions in the CuCoO series ( = Ca, Y, Ce) from CaCuCoO to YCuCoO to CeCuCoO, where the electrons are doped in the order from -site (Co → Co) to '-site (Cu → Cu).