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

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 degrees 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 MgB2 wires was more than one order of magnitude higher than that of the undoped MgB2 wire at 5 K and 6.6 T (1.46-3.82 kA/cm(2) vs. 0.11 kA/cm(2)). (c) 2010 Elsevier B.V. All rights reserved.