Fabrication of ex situ processed MgB₂ wires using nano carbon doped powder

We fabricated ex situ MgB₂ wires using C-doped MgB₂ powder as a precursor in order to improve the core density of the wires and their C doping content. The C-doped powder was prepared with Mg, B, and nano carbon (NC) powders by the in situ technique and then MgB_2-xC_x (x = 0, 0.01, and 0.03) wires were fabricated by the ex situ technique using the powder-in-tube method. The phase formation, lattice change, and microstructure were characterized and correlated with the T_c and J_c variations. We observed that the ex situ wire had a higher core density than the in situ wire, however its morphology consisted of agglomerated particles, indicating that sintering and grain growth did not occur completely, even though the sintering was conducted at high temperature (1000 °C). As the C content increased, T_c decreased, while the decrease of J_c with increasing magnetic field became smaller. The J_c of MgB_1.97C_0.03 wire made by the ex situ technique was 3.34 kA/cm² at 6.6 T and 5 K which is comparable to that of the in situ wire (4.81 kA/cm² at 6.6 T and 5 K).