Critical current densities of high-Tc superconductors

While considering wire applications, three kinds of fabrication processes-solid reaction, film, and melt processes-were studied to improve the transport critical current densities (J_c) of high-T_c superconductors at liquid nitrogen temperature (77.3 K). In all three processes, a 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, a J_c of 4×10⁶ A/cm², which is considered useful for practical application, was obtained by fabricating good films with flat surfaces and c-axis-oriented single-like crystals. In the melt process, oriented polycrystalline BiSrCaCuO rods with J_c of 14800 A/cm² were fabricated. The magnetic field dependencies of the J_c of each sample were studied. In particular, thin films of YBaCuO were found to maintain the value of 10⁴ A/cm² even at 20 T