Improved critical current densities inB4C doped MgB2 based wires

Abstract

An improvement of the transport critical current density,Jc,of MgB2 wires was obtained after the addition of 10 wt%B4C powders, afterreaction at 800 °C: Jc valuesof 1 × 104 A cm−2 at 4.2 K and 9 T were obtained for wires of 1.11 mm diameter in a Fematrix. The starting mixture of Mg and B was doped with submicrometricB4C, the ratio beingMg:B:B4C = 1:2:0.08, correspondingto 10 wt% B4C. For T>800 °C, adecrease of Jc was found, due to the reaction with the Fe sheath. In order to investigate theorigin of the improvement of the transport properties for heat treatments up to800 °C, x-ray diffraction measurements were performed. A decrease of the lattice constanta from 3.0854 to 3.0797 Å was found, thus suggesting an effect of the substitution of carbon on theproperties of the wires. A comparison with the literature data shows that the addition ofB4C powders leads to the second highest improvement ofJc reported so far after SiC, thus constituting an alternative for future applications.