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

由于Ca_2-x&Gt；Na_xCuO_2Cl2容易解理和结构不扭曲，是角分辨光电子能谱(ARPES)和扫描隧道显微镜(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，用同步X射线衍射法对化学反应进行了原位观察。x=0.1样品(T_c=13K)的ARPES数据最有可能用“化学势移动”来描述，这与La_&lt；2-x&gt；SrxCuO_4的“钉扎化学势”形成了对比。在x=0.08和0.12样品的STM图像中观察到了纳米级的片状和河流状的不规则波纹。状态密度随图像对比度的不同而变化，表明相分离为金属区和绝缘区。首次在更高的压力下合成了具有覆盖层成分的粉末样品，最高可达10 Gpa。对排列好的粉末样品进行了μSR研究。已知Ca2CuO2Cl2是一种T_N=250K的反铁磁体。在Ca_&lt；2-x&gt；Na_xCuO_2Cl2中，T_N随x的增加而迅速下降，在x=0.01时消失。对前者的单晶和粉末样品的同步辐射X射线衍射谱表明，在金属-绝缘体转变温度，伴随着镍价电荷歧化的结构转变。BiMnO_3中6s^2孤对的存在使该化合物成为一种新颖的铁磁性铁电化合物。在该化合物的启发下，对BiCoO_3、BiCrO_3、BiNiO_3进行了研究。所有这些材料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.