Preparation of High-Tc Superconducting Bi-Ca-Sr-Cu-O Ceramics by the Melt Quenching Method

Superconducting Bi-Ca-Sr-Cu-O ceramics with T_c(onset)=102 K and T_c(zero)=92 K were prepared by a melt quenching method, in which the melt of nominal composition BiCaSrCu₂O_x was first quenched and then annealed at 800∼ 850°C for 24 h in oxygen atmosphere. It was found that the rapidly cooled samples after annealing show high T_c and sharp superconducting transition, but the samples slowly cooled in the furnace after annealing show low T_c and broad transition with a tail. The critical current density at 77 K in the zero magnetic field for the rapidly cooled sample after annealing at 800°C was 102 A/cm².