Single crystal growth of oxycloride superconductor at high pressures and investigation of the physical properties

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Because of the easy cleavage and undistorted structure, Ca_<2-x>Na_xCuO_2Cl_2 is an ideal compound for angle resolved photoemission spectroscopy (ARPES) and STM measurements. These measurements were performed on single crystal samples grown at high pressures based on the in-situ observation of the chemical reaction by means of synchrotron X-ray diffraction study.The ARPES data on x=0.1 sample (T_c=13K) were most likely described by a "chemical potential shift" which contrasts with the "pinned chemical potential" reported for La_<2-x>Sr_xCuO_4. Nano-scale patch-like and river-like irregular corrugations were observed in the STM images take for x=0.08 and 0.12 samples. The density of states changed depending on the contrast of the images, suggesting the phase separation into metallic and insulating regions.Powder samples with the overdope composition were prepared for the first time by synthesizing at even higher pressures up to 10 Gpa. μ SR studies were performed on aligned powder samples. Ca_2CuO_2Cl_2 had been known to be an antiferromagnet with T_N=250K. In Ca_<2-x>Na_xCuO_2Cl_2, T_N decreased rapidly with increasing x and disappeared at x=0.01.Single crystals of PrNiO_3 and BiMnO_3 were grown at high pressures with the technique developed in this project. Synchrotron X-ray diffractions on both single crystal and powder samples of the former revealed the presence of a structural transition accompanied by the charge disproportionation of Ni valence at the metal-insulator transition temperature. The presence of 6s^2 lone pairs in BiMnO_3 makes this compound novel ferromagnetic ferroelectric. Inspired by this compound, BiCoO_3, BiCrO_3, BiNiO_3 were investigated. All of these had distorted perovskite structures.