Enhancement of Critical Current Density in Graphite Doped MgB₂ Wires

Graphite doped MgB_2-xC_x (x = 0.00, 0.05, 0.10) wires were fabricated via the in situ powder-in-tube method in flowing argon by using low carbon steel tubes as the sheath materials. With the increase of graphite concentration, the amount of unreacted graphite in the core area increases, and the average grain size of MgB₂ decreases. It is found that the critical current density J_c can be significantly improved by graphite doping. The MgB₂ wire with x = 0.05 exhibits the best J_c value of 16710A/cm² at 6K, 4.5T, but the MgB_1.9C_0.1 wire has the highest J_c value of 2060 A/cm² at 6K, 8T. It is suggested that the enhancement of J_c is due to not only the improvement of the microstructure features but also the introduction of pinning centres.