GROWTH OF LARGE ISOMETRIC YBA2CU3OX SINGLE-CRYSTALS FROM COEXISTING REGION OF SOLID WITH MELT IN Y2O3 CRUCIBLES

Large isometric single crystals of oxide superconductor YBa2Cu3Ox (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).