Pinning Behavior in Bulk MgB2 Prepared Using Boron Powder Refined Via High-Energy Ultra-Sonication

We successfully refined a cheap commercial boron powder by means of high-energy ultra-sonication and utilized it in synthesis of bulk MgB 2 . Rietveld phase analysis of X-ray diffraction pattern revealed completely formed MgB 2 with a low amount of MgO. MgB 2 bulk prepared of boron ultra-sonicated in ethanol for 15 min showed self-field J c of around 300 kA/cm 2 at 20 K without any compromise in T c (~39 K). Pinning analysis based on Dew-Hughes expression showed major pinning contribution from grain-boundary pinning (~95.5%), along with a slight contribution from point pinning (4.5%). The microstructure study detected a system of large MgB 2 grains (hundreds nm large) and 10–20 nm sized particles, possibly Mg-B-O, formed at MgB 2 grain boundaries.