Fabrication and Properties of Flexible Tapes of High-Tc Bi-(Pb)-Sr-Ca-Cu-O Superconductors

Abstract

The discovery of high-T_c oxide superconductors, especially of the Ba₂YCu₃O₇, Bi-Sr-Ca-Cu-O² and Tl-Ba-Ca-Cu-O³ compounds, which show superconductivity above liquid nitrogen temperature, has had great impact not only basic physics but also on the field of superconductor application. The application of a compound superconductor to a superconducting magnet requires the winding of tape or wire conductors with sufficient flexibility into a solenoid. Among the various superconducting compounds having intrinsic brittleness, Nb₃Sn and V₃Ga compounds with A15 structure have been successfully fabricated into a tape or wire form by the so-called ‘bronze process’ which utilizes the solid state reaction. The oxide high-T_c superconductors are also intrinsically brittle, and special techniques must be developed for making tape or wire conductors. The studies on stress dependence of the high-T_c oxide superconductors are also practical interest, because the superconductor must withstand various stresses caused by coil winding, Lorentz force etc. Standard ceramic processes of mixing powders and organic formulations are applicable for preparing of high-T_c oxide superconductor tape or wire, as demonstrated for Ba₂YCu₃O₇ compound.^4,5 However, these tapes or wires became rather brittle after the final sintering process.