Effect of MgB4 Addition on the Superconducting Properties of Polycrystalline MgB2

The objective of this work is to improve the flux pinning performance of bulk MgB2 superconductors by dispersing nanometer-sized MgB4 particles. The high quality MgB4 material was produced, and the MgO rest in the powder was removed by HNO3 (1 M) leaching. Several bulk polycrystalline samples were fabricated by means of the solid state reaction method with compositions MgB2 + x wt% of MgB4 (x=0, 2, 5, and 10) at 775oC in pure argon atmosphere. X-ray diffraction indicated single phase and homogenous MgB2 bulks when MgB4 content was below 5wt%. The superconducting transitions were sharp at low MgB4 concentrations. The critical current density, Jc, depend on the MgB4 content in the MgB2 composite. The MgB2 sample with 2wt% of MgB4 processed at 775oC for 3 h showed the critical current density of 300 kA cm-2 at 20 K in self field.