STUDY ON THE SUBSTRATE SINGLE CRYSTALS FOR HIGH TEMPERATURE SUPERCONDUCTING FILMS

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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.