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

Abstract

Pure and nano-Cu doped MgB2/Fe superconducting wires were prepared by in situ powder-in-tube method at different temperatures (550-675 degrees 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 degrees 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 degrees C exhibited a transport J(C) quite comparable to that of the pure sample processed at 650 degrees C, which shows that high quality MgB2 conductors can be produced even at 550 degrees C with minor Cu doping.