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

Abstract

We selected polyacrylonitrile (PAN, –[C3H3N]–) as an O-free organic dopant and fabricated C-doped MgB2 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 1h in a flowing Ar gas.The PAN doping decreased the critical temperature (Tc) and a-axis lattice parameter, but significantly improved the critical current density (Jc) in high fields, upper critical field (Hc2), and irreversibility field (Hirr) 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 Jc of the PAN-doped MgB2 wires was more than one order of magnitude higher than that of the undoped MgB2 wire at 5K and 6.6T (1.46–3.82kA/cm2 vs. 0.11kA/cm2).