Enhanced Critical Current Transport and Improved Grain Connectivity of in-situ MgB2 Wires Doped with Cu2Se

Cu2Se-doped MgB2/Nb/Cu composite superconducting wires are successfully fabricated using the in-situ Powder-in-Tube (PIT) method. The effects of varying Cu2Se doping levels (0, 5, and 10 wt.%) on the microstructure, phase composition, and superconducting properties of the wires are systematically investigated. Microstructural analysis reveals that Cu2Se completely reacts with Mg during the sintering process to form MgSe and MgCu2. These nanoscale secondary phases are uniformly dispersed within the matrix and work synergistically to bridge intergranular gaps and optimize the superconducting electron transport paths. Furthermore, Cu2Se and its reaction products provide heterogeneous nucleation sites and regulate crystal growth, promoting MgB2 grain nucleation and growth and enhancing core density and grain connectivity. Superconducting performance tests demonstrate that Cu2Se doping significantly improves the critical current (Ic) of the wires under low-temperature and zero-field conditions. Notably, the 5 wt.% Cu2Se-doped sample exhibits the best overall performance, achieving an Ic of 252.1 A at 10 K under zero external field, approximately 2.5 times that of the undoped MgB2 wire. The enhancement is primarily attributed to two factors. First, the synergistic effect of deformation densification from the PIT process and doping-induced microstructural optimization improves the superconducting current transport paths. Second, the significant improvement in intergranular connectivity and core density effectively overcomes the weak-link effect, which substantially increases the current-carrying capacity of the wires.