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 1.6 Pb 0.4 Sr 1.6 Ca 2 Cu 2.8 O y with a T c of 103 K was 4.81 g/cm 3 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/cm 3 , 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/cm 2 .