Critical Current Density Characteristics in Superconducting Y_xBa_1-xCu-Oxides

The transition temperature, Tc, and the critical current density, Jc(B), at 4.2 K have been studied in high-Tc YxBa1-xCu-Oxide system. Previously observed two maxima in Tc were reexamined. A very large anisotropy, very fast degradations at low fields, and a large hysteresis in Jc(B) have been observed in this system. The cause of the large anisotropy might be the strong c-axis orientation perpendicular to the pressed surface and the low dimensionality of the crystal structure of this material. Although Jc value is very small, the decrease in Jc from 2 to 27 T is only about 20 %, which shows a high potential for practical use at high fields when Jc is raised by the introduction of strong pinning centers in this material.