Flux Pinning and Superconducting Properties of Bulk MgB₂ with MgB₄ Addition

The improved performance of bulk MgB₂ material with added nanometer‐sized MgB₄ particles is presented. Bulk polycrystalline MgB₂ samples with varying amount of MgB₄ x (x = 0, 1, 2, 3, 4, 5, and 10 wt%) are fabricated by solid‐state sintering at 775 °C for 3 h in pure argon gas. Microstructural studies indicate formation of nanometer‐sized grains when MgB₄ is added. Density of nano‐grains is inversely proportional to the MgB₄ content. The MgB₂ sample with 1 wt% of MgB₄ shows the best performance, with its self‐field critical current density reaching 385 and 315 kAcm⁻² at 15 and 20 K, respectively. Flux pinning diagrams reveal the domination of grain boundary pinning mechanism.