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

本研究获得的主要课题如下。(1)通过原位高温x射线衍射测量，澄清了铋基铜高温超导体的赝二元相图，该相图可能与铊基铜高温超导体的赝二元相图相似。澄清了一种新的不稳定铜酸铋的稳定性。阐明了非晶铋基铜的结晶过程。通过时间分辨x射线衍射测量估计了结晶的活化能。(2)新开发了铊基铜高温超导体的立式电炉和密闭气氛生长技术。研制了一种新型的铊基铜高温超导体生长电池。(3)制备出了高质量的铊基铜酸盐高温超导体大单晶，特别是铊-氧双层铜酸盐。在可控的氧分压气氛下，通过退火得到了重掺杂和微掺杂的铊-氧双层铜铜高温超导体。另一种基于铊的铜高温超导体现在也在尝试生长。(4)测定了生长晶体的涡流熔点、不可逆磁场和上临界场。澄清了铜超导体中的涡旋行为，并获得了一些新的结果来解释高温超导的机理。目前，国内外许多学者正在利用该晶体进行扫描隧道显微镜、光电发射测量、德哈斯-凡阿尔芬效应测量等方面的研究。

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.