Critical current enhancement in Bi-2223/Ag superconducting tapes by controlling its first sintering process

Microstructural evolution of the Bi-2223 phase, liquid phase and secondary phase in the first sintering process has been studied by means of XRD and SEM/EDS. Experiments show that the first sintering temperature and time have a great influence on the Bi-2223 phase formation. The cooling rate after the first sintering process determines the type and grain size of the secondary phases, which in turn decides the critical current of the fully reacted tapes. The fast cooled sample contains a few secondary phase particles with very small size, whereas the slow cooled sample produces large CuO particles. The (Ca,Sr)2CuO3 and (Ca,Sr)14Cu24O41 phases are easy to deform, while CuO phase particle has a high hardness and is difficult to deform during uniaxial press. The critical current is largely improved by controlling the cooling rate of the first sintering process.

Research highlights▶ The cooling rate in the first sintering decides the Ic of the final tapes. ▶ Fast cooled sample contains a few secondary phase particles. ▶ Large CuO particles formed in the slowly cooled sample. ▶ The 2:1 and 14:24 phases are easy to deform, while CuO has higher hardness. ▶ 10 h is the critical point during the first sintering process.