STUDY ON THE SUBSTRATE SINGLE CRYSTALS FOR HIGH TEMPERATURE SUPERCONDUCTING FILMS

1.采用MAO和SrTiO_3单晶作为超导氧化物薄膜的衬底晶体。然而，它们不是合适的晶体，因为它们的晶胞常数与超导YBCO薄膜的晶胞常数不匹配。在本研究中，我们试图通过在基片中加入CaTiO_3和BaTiO_3来改变SrTiO_3的晶胞常数，以获得更适合于基片的单晶。此外，还用浮区法生长了Nd1-X&Gt；YxAlO3单晶的固溶体，以考察该化合物是否可用于衬底。用X射线衍射仪和光学显微镜测量了外加化合物对其晶体结构和晶胞常数的影响。在两种体系中都观察到了晶胞常数的降低，分别为：Sr_&lt；1-X&GT；Ca_xTiO_3系；在Sr_&lt；1-X&gt；Ca_xTiO_3系统中，以1 mm/hr的生长速度生长的晶体直径为5 mm，长25 mm，透明，呈淡黄色。观察到Ca5.21at%的单晶在四方相和立方相之间发生了可逆转变。在Sr_1-X&GT；BaxTiO_3系统中，以1 mm/hr的生长速度生长的晶体直径为8 mm，长30 mm，透明，呈淡黄色。由于在两个系统中都观察到了域结构，因此有必要保护以增长域结构。在Ndlt；1-X&Gt；Y_xAlO_3系统中，当x=0.32时，生长的晶体呈透明的紫色。从生长的薄膜的表征可以清楚地看出，生长的薄膜是以a轴取向的。这一结果表明该晶体将适合作为衬底晶体。

1.Single crystals of Mao and SrTiO_3 have been used as the substrate crystal for the superconducting oxide films. However, they are not suitable crystals because the cell constant of these crystals do not fit the cell constant of superconducting YBCO thin film. In this study, we have tried to get more suitable single crystal for substrate changing the cell constant of SrTiO_3 by adding CaTiO_3 and BaTiO_3 into that. Also, the solid solution of Nd_<1-X>Y_XAlO_3 single crystal has been grown by floating zone method to investigate whether this compound would be useful for substrate or not. The properties of crystal stracture and cell constant due to adding the foreign compounds were measured by using XRD and optical microscopy. The decrease of cell constants were observed in both Sr_<1-X>Ca_XTiO_3 system and Sr_<1-X>Ba_XTiO_3 system. In Sr_<1-X>Ca_XTiO_3 system, the as-grown crystal by applying the growth rate of 1 mm/hr was 5 mm in diameter by 25 mm long, transparent and light yellow. It was observed that the single crystal of Ca 5.21at% of Ca was transformed reversibly between tetragonal phase and cubic phase. In Sr_<1-X>Ba_XTiO_3 system, the as-grown crystal by applying the growth rate of 1mm/hr was 8mm in diameter by 30 mm long, transparent and light yellow. As the domain structure were observed in the both systems, it is necessary to protect to grow the domain structure. In Nd_<1-X>Y_XAlO_3 system, as-grown crystal was transparent and purple color at x=0.3.2.The YBCO thin film was prepared on the single crystal of Nd_<2-X>Ce_XCuO_4 to see the probability for the substrate crystal. From the characterization of grown film, it was cleared that the grown film was oriented to a-axis. This result suggested this crystal will be suitable for substrate crystal.