抄録
Effects of impurity contents in starting materials of YBa2Cu3Ox (123) ceramics on the critical transition temperature, Tc, and the critical current density, Jc, were investigated. Specimens for measurements of Tc, and Jc were fabricated by sintering and melt-growth techniques using reagents of various purity grades. Superconducting properties were affected with the purity of starting materials as well as the preparation techniques. As for sintered specimens, Tc, and Jc values increased 87.4-89.6K and 140-317A/cm2 (at 77K, OT), respectively, with a decrease in impurity contents in starting materials. In the melt-growns pecimens, both Tc and Jc values were improved to be 90.0-92.9K and 235-960A/cm2, respectively. In these specimens, with lowering impurity contents, T. values increased whereas Jc values decreased. All the sintered specimens showed similar microstructures with randomly oriented plate-like 123 grains, irrespective of impurity contents. On the other hand, fine grained needle-like 123 crystals and spherulitic microstructures were observed, in the melt-grown specimens, in which the 123 grains became smaller with an increase in impurity contents.
