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

氯氧化物超导体的高压单晶生长及物理性能研究

基本信息

批准号：
13440111
负责人：
AZUMA Masaki
金额：
$ 8.7万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-13440111/
关键词：
High Temperature superconductor Oxychloride Single Crystal High Pressure synthesis Synchrotron Radiation X-ray Photoemission STM μSR アンダードープ

项目摘要

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.

Ca_ Na_xCuO_2Cl_2具有易断裂和结构不畸变的特点，<2-x>是角分辨光电子能谱（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的同步辐射X射线衍射原位观察化学反应的基础上进行的，x=0.1样品（T_c= 13 K）的ARPES数据很可能用“化学势位移”来描述，而La_ Sr_xCuO_4的“钉扎化学势”则相反<2-x>。对于x=0.08和0.12的样品，在STM图像中观察到纳米尺度的斑块状和河流状不规则波纹。态密度的变化取决于图像的对比度，表明相分离成金属和绝缘区域。首次通过在高达10 Gpa的更高压力下合成制备了具有过掺杂组合物的粉末样品。对对齐的粉末样品进行μ SR研究。Ca_2CuO_2Cl_2是一种反铁磁体，T_N= 250 K。在Ca_ Na_xCuO_2Cl_2中<2-x>，T_N随x的增加而迅速下降，当x= 0.01时T_N消失。前者的单晶和粉末样品上的同步辐射X射线衍射揭示了在金属-绝缘体转变温度下伴随着Ni价态的电荷交换的结构转变的存在。BiMnO_3中6s^2孤对电子的存在使其成为一种新型的铁磁铁电体。在此基础上，研究了BiCoO_3，BiCrO_3，BiNiO_3等化合物。所有这些都具有扭曲的钙钛矿结构。