Enhancement in the critical current density of C-Doped MgB ₂ wire using a polyacrylic acid dopant

C-doped MgB ₂ wires were fabricated from a polyacrylic acid (PAA) using a conventional in-situ PIT technique. The effects of the PAA content on the lattice parameter, microstructure, critical temperature (T _c and critical current density (J _c were examined. With increasing PAA content, the amount of MgO in the sample increased but the crystallinity, a-axis lattice parameter, and T _c of MgB ₂ wires decreased, indicating that the C that decomposed from PAA during heat treatment had substituted for B. All doped samples exhibited a higher Jc than the undoped sample at high magnetic field, and the J _cB property improved with increasing PAA content: for the 7 wt% doped sample, the Jc was approximately 3-times higher than that of the pristine sample (1.28 kA/cm ² vs. 3.43 kA/cm ² at 5 K and 6.6 T. The improved J _cB of the doped sample was attributed to the decreased grain size, enlarged lattice distortion and increased C doping level.