Improved critical current densities in B4C doped MgB2 based wires

An improvement of the transport critical current density, J(c), of MgB2 wires was obtained after the addition of 10 wt% B4C powders, after reaction at 800 degrees C: J(c) values of 1 x 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 B4C, the ratio being Mg:B:B4C = 1:2:0.08, corresponding to 10 wt% B4C. For T > 800 degrees 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 degrees C, x-ray diffraction measurements were performed. A decrease of the lattice constant a from 3.0854 to 3.0797 angstrom 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 B4C powders leads to the second highest improvement of J(c) reported so far after SiC, thus constituting an alternative for future applications.