Improvement of the current carrying capability of ex situ MgB2 wires by normal particle additions

A wide variety of powders, including Nb, Ti, Zr, Hf and W, metal oxides like Nb2O5, Ti2O5, V2O5 and other compounds like SiC, SrCO3 and boron nitride, have all been used at the 10 wt% level as additions into commercial MgB2 powder for the fabrication of single-core, ex situ wires using groove and two-axial rolling deformation and final heat treatment at 950degreesC/0.5 h in Ar. Transport current measurements have shown that metal particle addition leads to an especially significant improvement in current carrying capacity. The presence of normal particles influences both the resistivity and also the thermal conductivity of the MgB2 core, and the improved internal stability may be responsible for the increased critical current values. This observation may be very important for future development of practical MgB2 composite superconducting wires.