Fabrication and superconductivity of BPSCCO-2223 oxide bulk by a new design composite

Abstract

We have studied a newly designed BPSCCO-2223 bulk composed of mono-cored BPSCCO-2223/Ag sheath filaments. The composite structure design of the combination of BPSCCO-2223 and mono-cored filaments was newly developed with the aim of protection when bulk material is used as a current feeder for large-scale applications. The composites were made by alternately stacking BPSCCO-2223 oxide-cored Ag sheath filaments and the oxide powder by the powder-in-tube (PIT) method, and then the prepared samples were sintered at 840 °C for 50 h. Then, a cold isosatic pressing (CIP) process was applied and they were re-sintered at 840 °C for 50 h. As a result, the maximum transport current (Ic) value of the composite bulk, which is composed of 24 mono-cored sheath filaments of 0.4 mm in diameter, was estimated to be about 240 A at 4.2 K and 0 T. This Ic value was about three times higher than that of a conventional bulk, and the value of the PIT filaments composite bulk was also higher than that of the Ag wires composite bulk. This is why good c-axis oriented and densely structured BPSCCO-2223 plate-like grains were formed on both the outer and inner interface between the oxide and Ag in the PIT filaments. Furthermore, we confirmed that transport current was flowed into the PIT filaments composite bulk after forcing a fracture by the bending test. We guessed that the PIT filaments could act as a bypass for the fracture of the bulk. We thought that a new design of the composite bulk in this study was interesting in terms of safety precautions for large-scale applications.