Enhancing the critical current properties of internal Mg diffusion-processed MgB ₂ wires by Mg addition

The internal Mg diffusion (IMD) process produces a high-density MgB ₂ layer with high critical current properties, which makes it an attractive and promising method for fabricating MgB ₂ wires. We have obtained high critical current properties in our previous research. However, IMD-processed MgB ₂ wires can have unreacted B particles remain in the reacted layer due to the long Mg diffusion distance in the B layer during heat treatment. A reduction in the amount of unreacted B particles is expected to enhance the critical current properties. In this study, we attempted to disperse Mg powder in the B layer as an additive in order to decrease the Mg diffusion distance. We found that a 6 mol% Mg powder addition to a B layer drastically decreased the amount of unreacted B particles and enhanced the critical current density to twice the value for IMD-processed MgB ₂ wire with no Mg powder added. An analysis is presented that relates the microstructure to the critical current density.