Pseudobinary phase dicgram and larg high-quality single crystal growth of thallium-based cuprate high temperature superconductors

本研究的主要内容如下：(1)用原位高温X射线衍射法确定了铋系铜酸盐高温超导体的准二元相图，它可能与铊系高温超导体的相图相似。还阐明了一种新的不稳定的铜酸铋盐的稳定性。阐明了非晶态铋基铜酸盐的晶化过程。用时间分辨X射线衍射法估算了晶化活化能。(2)发展了一种新型的立式电炉和封闭气氛生长技术，用于制备高温超导体。研制了一种新型的高蒸汽压、有毒的铊基铜酸盐高温超导体生长池。(3)生长出了大尺寸、高质量的铊基铜酸盐高温超导体单晶，特别是铊-氧双层铜酸盐。在控制氧分压的气氛下，通过退火获得了重掺杂和轻微过度掺杂的单一的铊-氧双层铜酸盐高温超导体。对生长出的晶体的涡旋熔点、不可逆磁场和上临界场进行了测定。阐明了铜酸盐超导体中的涡旋行为，并得到了一些新的结果来解释高温超导的机制。利用生长的晶体进行扫描隧道显微镜、光电子能谱测量、德哈斯-范阿尔芬效应测量等方面的研究正在与国内外许多合作者一起进行。

Main topics obtained in this study are described below.(1) Pseudobinary phase diagrams of the bismuth-based cuprate high temperature superconductors, which may be similar to that of that of the thallium-based ones, have been clarified by in-situ high temperature X-ray diffraction measurements. stability of a new unstable bismuth cuprate has been also clarified. Crystallization processes of amorphous bismuth-based cuprate have been clarified. The activation energy for the crystallization has been estimated by the time-resolved X-ray diffraction measurements.(2) Vertical-type electric furnace and closed-atmosphere growth technique for the thallium-based cuprate high temperature superconductors have been newly developed. A new growth cell for the thallium-based cuprate high temperature superconductors, which are toxic and have high vapor pressure, has been developed.(3) Large high-quality single crystals of the thallium-based cuprate high temperature superconductors, especially thallium-oxygen double layered cuprates, have been grown. Heavily and slightly overdoped single of the thallium-oxygen double layered cuprate high temperature superconductor have been obtained by annealing under the controlled atmosphere of oxygen partial pressure. The other thallium-based cuprate high temperature superconductors are also now tried to grow.(4) Vortex melting points, irreversible magnetic fields and upper critical fields of the grown crystals have been determined. Vortex behaviors in the cuprate superconductors have been clarified and some new results to resolve a mechanism of the high temperature superconductivity are also obtained. Investigations on the scanning tunneling microscopy, photoemission measurements, de Haas-van Alphen effect measurements using the grown crystals are now going on with many domestic and foreign collaborators.