Improved critical current densities in B4C doped MgB2based wires

An improvement of the transport critical current density, J c , of MgB 2 wires was obtained after the addition of 10 wt% B 4 C powders, after reaction at 800 °C: J c values of 1 × 10 4 A cm −2 at 4.2 K and 9 T were obtained for wires of 1.11 mm diameter in a Fe matrix. The starting mixture of Mg and B was doped with submicrometric B 4 C, the ratio being Mg:B:B 4 C = 1:2:0.08, corresponding to 10 wt% B 4 C. For T >800 °C, a decrease of J c was found, due to the reaction with the Fe sheath. In order to investigate the origin of the improvement of the transport properties for heat treatments up to 800 °C, x-ray diffraction measurements were performed. A decrease of the lattice constant a from 3.0854 to 3.0797 Å was found, thus suggesting an effect of the substitution of carbon on the properties of the wires. A comparison with the literature data shows that the addition of B 4 C powders leads to the second highest improvement of J c reported so far after SiC, thus constituting an alternative for future applications.