Densification and Grain-Orientation of Bi-Pb-Sr-Ca-Cu-O Superconductors by Hot-Pressing

The bulk density of a normal sintered sample of Bi_1.6Pb_0.4Sr_1.6Ca₂Cu_2.8O_y with a T_c of 103 K was 4.81 g/cm³ and shrinkage of the sample was barely observable. By hot-pressing at a pressure of 39 MPa at 800°C in a vacuum of 5× 10^-5 Torr for 2 h, the bulk density of the hot-pressed sample reached 6.21 g/cm³, which was over 95% of the theoretical density, and the T_c was 72 K. The grains were oriented with the c-axis along the pressing axis. After annealing at 835°C in air for 40 h, the T_c was improved to 108 K and the critical current density at 77 K was found to be 731 A/cm².