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

由于Ca_<2-x>Na_xCuO_2Cl_2具有易解理和不变形的结构，是角分辨光发射光谱（ARPES）和STM测量的理想化合物。这些测量是在高压下生长的单晶样品上进行的，基于同步加速器x射线衍射研究的化学反应的现场观察。x=0.1样品（T_c=13K）的ARPES数据与La_<2-x>Sr_xCuO_4报告的“固定化学势”形成对比，最有可能用“化学势位移”来描述。在x=0.08和0.12样品的STM图像中观察到纳米级斑块状和河流状不规则波纹。状态密度随图像对比度的变化而变化，表明相分离为金属区和绝缘区。在高达10gpa的高压下，首次合成了具有超掺杂成分的粉末样品。对排列好的粉末样品进行了μ SR研究。已知Ca_2CuO_2Cl_2是T_N=250K的反铁磁体。在Ca_<2-x>Na_xCuO_2Cl_2中，T_N随x的增大而迅速减小，在x=0.01时消失。在高压条件下制备了PrNiO_3和BiMnO_3单晶。对单晶和粉末样品的同步x射线衍射显示，在金属-绝缘体转变温度下，存在结构转变，并伴有Ni价的电荷歧化。在BiMnO_3中存在6s^2孤电子对，使这种化合物具有新颖的铁磁性和铁电性。受此化合物的启发，对BiCoO_3、BiCrO_3、BiNiO_3进行了研究。所有这些都具有扭曲的钙钛矿结构。

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.