Progress in Critical Current Density (J (c) ) in Sintered MgB2 Bulks

The present paper focuses on methods of further improving the flux pinning and critical current density of disk-shaped MgB2 bulk superconductors by adding excess Mg metal in combination with an optimum silver content and optimized processing conditions. Bulk MgB2 samples were produced by in situ solid-state reaction in Ar gas ambient using high purity commercial powders of Mg metal and 1.5 wt% carbon-coated amorphous B powders mixed in a fixed ratio of Mg/B = 1.1:2. Further, 4 wt% silver was added to improve flux pinning as well as mechanical performance of the bulk MgB2 material. The magnetization measurements confirmed a sharp superconducting transition with T (c,onset) at around 37 K, which is only by 1 K lower than in bulk MgB2 material produced without carbon-coated amorphous boron. The critical current density (J (c) ) values significantly improved in the MgB2 material with 4 wt% of silver and 1.5 wt% of carbon-coated amorphous boron, sintered at 775 C-ay for 3 h. At 20 K, this sample showed J (c) at around 500 and 350 kA/cm(2) in the self-field and 1 T, respectively, which makes it suitable for several industrial applications.