Growth of Large Isometric YBa2Cu3Ox Single Crystals from Coexisting Region of Solid with Melt in Y2O3 Crucibles

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Abstract
Large isometric single crystals of oxide superconductor YBa2Cu3O x (YBCO) have been grown from a mixed region of solid Y2BaCuO5 and melt. The crystals possess sharp, shiny habits with a maximum thickness of about 7 mm along the c-axis. The best growth condition is that wherein the solvent composition is 7BaCuO2·11CuO which is close to the binary eutectic of BaCuO2-CuO, and the optimum concentration of the growth system is that wherein the ratio of YBCO to 7BaCuO2·11CuO is 64:36. The use of a Y2O3-crucible prevents contamination from containers during growth, and facilitates the synthesis of high-purity crystals. Temperature gradient and seed crystals are both effective for controlling nucleation. The annealed crystals show a sharp superconductive transition at 91 K. The temperature dependence of the resistivities is found to be metallic in the ab- as well as the c-direction. Sufficient diamagnetism is manifested as a sharp transition at T c and a complete shielding effect below T c.