Effect of boron precursor ultra-sonicated in hexane medium on the critical current density of sintered bulk MgB₂

The large coherence length of MgB2 material allows large defects such as grain boundaries to act as strong pinning centres. As an alternative to the high-cost commercial nano precursors, we used a novel ultra-sonication technique to refine a cheap rough boron precursor and avoid the use of the expensive commercial nano amorphous boron powder. Recent novel low-cost ultra-sonication technique proved to improve the critical current density, J c, of MgB2. Here, we discuss the consequences of ultra-sonication duration in hexane medium on the boron precursor as well as the superconducting properties of MgB2 bulks. XRD revealed small peaks corresponding to unreacted Mg. First derivative of susceptibility was plotted as a function of temperature to explain the Tc,onset and ΔTc. J c was found to grow if the MgB2 bulk was prepared of boron ultra-sonicated for up to 30 minutes and then reduced with further boron ultra-sonication (60 minutes). SEM micrographs showed that boron powder subjected to longer ultra-sonication resulted in agglomeration of broken boron particles, forming large MgB2 grains. Based on the comparison of superconducting properties with previous results, we speculate that viscosity of the ultra-sonication medium might have a crucial role in the refinement of boron precursor powder.