Ex Situ MgB2 Superconducting Tape with Very High Critical Current Density by Using Low-Temperature Sintering Precursor Powders

Ex situ MgB2 is usually considered as with lower critical current density (J(c)) compared to the in situ one due to much worse inter-granular connectivity. In this work, we reported the fabrication of ex situ MgB2 superconducting tape without dopants using Monel as sheath materials and Nb as the barrier, which has an excellent J(c) of 705 A/mm(2) at 4.2 K under 4 T, almost as same as the in situ MgB2 wires. Massive and high-quality precursor powders with small grain sizes and quite low oxygen content were sintered at relatively low temperature and short time, 580 degrees C for 3 h. The effects of heat-treatment conditions and tape thickness on the microstructure and J(c) of ex situ MgB2 tapes were discussed. The results suggested that the improvement of grains-connectivity was responsible to the excellent J(c) properties of ex situ MgB2 tape.