Significant enhancement of flux pinning in MgB2/Fe/Cu superconducting wires fabricated by in situ powder-in-tube method

Dense MgB2/Fe/Cu wires with and without Zr doping were successfully prepared through the in situ powder-in-tube (PIT) method. MgB2/Fe/Cu wires were sintered at 650-850 °C for 2 h in argon. Critical current density (Jc) of the wires was measured at different temperatures in the magnetic field up to 8 T by standard four probe method. As shown by inductive measurements, the heat treatment temperature has an obvious influence on flux pinning of MgB2 wire. Also it is found that the flux pinning in MgB2 wire can be remarkably improved by Zr doping. The microstructure observation for MgB2 wires shows that MgB2/Fe/Cu wire with Zr doping has better grain connectivity and higher density than other samples. The mechanism leading to high transport critical current densities of MgB2/Fe/Cu wires based on MgB2 grain size is discussed. The results indicate that the Jc can be further improved to meet the requirement for applications by optimizing the process conditions.