Critical current densities of high-Tc superconductors

The most important property affecting the usefulness high-T _c superconductors is the critical current density. With wire applications in mind, three kinds of fabrication process, solid reaction, film, and melt, were studied to improve the transport critical current densities (J_c) at liquid nitrogen temperatures (77.3 K). In all three processes, J_c above 10⁴ A/cm² was obtained without an applied magnetic field. In the solid-reaction process, silver-sheathed BiPbSrCaCuO tapes with J_c of 12600 A/cm² were fabricated. The homogenization of the high-T_c phase (110 K), preferred alignment of the grains, and good contact at the grain boundaries resulted in the improvement of J_c . In thin-film YBaCuO, J_c of 4 ×10⁶ A/cm² was obtained by fabricating films with a flat surface and c-axis-oriented single-like crystals. In the melt process, oriented polycrystalline BiSrCaCuO rods with J_c of 14800 A/cm² were fabricated. Magnetic field dependencies of the J_c of each sample were studied. Thin films of YBaCuO maintained the value of 10⁴ A/cm² even in 20 T