In our earlier studies, we improved the critical current density (J_c) as well as the mechanical performance of disk-shaped MgB₂ bulk superconductors by adapting various innovative strategies including optimization of sintering temperature, optimization of sintering time, optimization of silver addition, addition of nano MgB₄, utilization of nano boron, optimization of carbon encapsulated boron, combined Mg excess and carbon encapsulated boron, carbon encapsulated boron with Dy₂O₃ additions etc. From this extensive study, it got clear that the nanoscopic boron is crucial for improving the performance of bulk MgB₂. Production cost of such a precursor is 3 times higher compared to use of the commercial boron. To reduce the production cost and improve the performance of bulk MgB₂, we utilized a novel low-cost technique, “high-energy ultra-sonication” and produced the nanoscale  boron powders in various solvents, like ethanol, hexane, and water for various times, from 0 to 45 min. The bulk MgB₂ material was prepared by sintering process, 3 h at 775 ^oC. All samples showed sharp superconducting transitions close to 39 K with DT_c less than 0.7 K. These studies revealed that 15 min and 30 min of boron ultra-sonication in ethanol and distilled water, respectively, resulted in J_c value of 300 kA/cm², which is 35% improvement compared to reference MgB₂. Boron ultra-sonication in hexane showed only 20% improvement. A long durations of ultra-sonication led to agglomeration of boron particles, which resulted in huge MgB₂ grains and reduction of T_c and J_c. These results can be correlated with viscosity of the employed media. Viscosity of ethanol and distilled water is about 1 cP, which is trice that of hexane (0.29 cP). We will explain the improved performance of ultra-sonicated boron based on microstructure changes in the final product.

Keywords: MgB2, Ultra-Sonicated Born , Low-cost and Improved Jc, Flux Pinning