Influence of nano-Cu additive on MgB₂ phase formation, processing temperature, and transport properties

Pure and nano-Cu doped MgB₂/Fe superconducting wires were prepared by in situ powder-in-tube method at different temperatures (550–675 °C). The phase formation, microstructure, and transport critical current density of the wires were investigated as a function of the heat-treatment temperature. A small amount of nano-Cu addition (2.5 wt %) was found to dramatically decrease the reaction temperature of magnesium and boron, forming MgB₂ without any degradation in the transport critical current. From x-ray diffraction and scanning electron microscopy analyses, it was found that the added Cu form a reacted phase Mg₂Cu with Mg which melts at around 550 °C. This liquid phase helps the formation of MgB₂ at a significant lower temperature with improved grain connectivity, grain size, and density. All Cu doped samples heat treated in the range of 550–650 °C exhibited a transport J_C quite comparable to that of the pure sample processed at 650 °C, which shows that high quality MgB₂ conductors can be produced even at 550 °C with minor Cu doping.