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/mm² 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 ^∘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.