Critical current density, morphology and microstructure of Ag-sheathed (Bi, Pb)2Sr2Ca2Cu3Ox tapes

Abstract The critical current density Jc, morphology and microstructure have been investigated on the Ag-sheathed (Bi, Pb)2Sr2Ca2Cu3O x superconducting tapes with overall tape thickness d (0.05mm≤d≤1.0 mm). The tapes were fabricated by a process of combined drawing and rolling with intermediate sintering steps, where no uniaxial pressing technique was applied. The thickness dependence of Jc at 77 K is characterized by three distinctive stages. At the first stage (0.2 mm≤d≤1.0 mm), Jc is increased gradually as d decreases, by the co-deformation between Ag sheath and ceramic core. At the second stage (0.1 mm≤d≤0.2 mm), it is raised sharply with decreasing d, by the densification of ceramic core itself in the tape. At the third stage (0.05 mm≤d≤0.1 mm), however, it is lowered by the distortion of the Ag/ceramics interface, which is caused by the extreme densification of ceramic core. A peak of Jc = 1.53×104 A/cm2 (77 K, 0 T) at d = 0.1 mm is explained by a competition between the improvement of grain connectivity and the disturbance in transport current path. The temperature dependence of Jc in zero external field is determined by a competition between the flux-creep-limited behavior and the weak-link-limited behavior, which are likely to be separated on a threshold value 1×104 A/cm2 (77 K, 0 T) in the sample.