Enhancement of Critical Current Density in Graphite Doped MgB2 Wires

Graphite doped MgB2-xCx (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 Jc can be significantly improved by graphite doping. The MgB2 wire with x = 0.05 exhibits the best Jc value of 16710A/cm2 at 6K, 4.5T, but the MgB1.9C0.1 wire has the highest Jc value of 2060 A/cm2 at 6K, 8T. It is suggested that the enhancement of Jc is due to not only the improvement of the microstructure features but also the introduction of pinning centres.