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

Abstract

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 Tc and a complete shielding effect below Tc.