The effect of intermediate layer densification on the critical current of a Bi-2223 superconducting joint

The effect of intermediate layer densification on the critical current (Ic) of Bi-2223 superconducting joints was quantitatively studied. First, we evaluated the phase purity, density, and intergrain critical current density (Jc) of Bi-2223 thick film samples simulating the intermediate layer. The samples were uniaxially pressed to increase the film density. After two heat treatments of the pressed film, an increase in Jc by the densification was achieved. Second, we fabricated superconducting joints by synthesizing an intermediate layer between two Bi-2223 tapes. Applying a uniform uniaxial pressure on the joint resulted in the formation of a homogenous structure. This process enables the reproducible fabrication of superconducting joints with high n values. The Ic of the superconducting joint was increased by intermediate pressing and two heat treatments. However, pressing at high pressures can mechanically damage filaments in the Bi-2223 tapes, leading to a decrease in Ic. Sample characterization showed that the optimum intermediate pressing pressure range to produce high Ic was 1.5–2 × 10^8 Pa. We confirmed that pressing densified the intermediate layer of the superconducting joints. Our experimental results and analyses reveal that densification of the intermediate layer increases the Ic of Bi-2223 superconducting joints.