O-free polyacrylonitrile doping to improve the Jc(B) and Hc2 of MgB2 wires

Abstract We selected polyacrylonitrile (PAN, –[C 3 H 3 N]–) as an O-free organic dopant and fabricated C-doped MgB 2 wires by in situ and powder-in-tube techniques. 0–5 wt.% PAN powders were uniformly mixed with B powder using a liquid mixing method. The precursor powders were mixed with Mg powder, filled into Fe tubes, and then drawn into wires. Sintering was performed at 900 °C for 1 h in a flowing Ar gas. The PAN doping decreased the critical temperature ( T c ) and a -axis lattice parameter, but significantly improved the critical current density ( J c ) in high fields, upper critical field ( H c2 ), and irreversibility field ( H irr ) performances. These results are attributed to the replacement of B sites with C by the PAN doping. Furthermore, as expected, the MgO amount did not increase as the doping content increased. The J c of the PAN-doped MgB 2 wires was more than one order of magnitude higher than that of the undoped MgB 2 wire at 5 K and 6.6 T (1.46–3.82 kA/cm 2 vs. 0.11 kA/cm 2 ).