Influence of boron powder purification on the connectivity of bulk MgB2

摘要

A key issue affecting the critical current density of MgB2 is the lack of full electrical connectivity. In situ MgB2 wires can be easily fabricated by reacting Mg powder with amorphous B powder, but such powders normally contain impurities such as B2O3 as a result of exposure to air. Here we introduce a practical method for removing B2O3 prior to making MgB2. X-ray diffraction and microstructure analysis show that removing B2O3 results in a decrease in MgO from 5.3 to 1.5 mol% in the final reacted MgB2. Normal state transport measurements using the Rowell analysis indicate that the active current-carrying area fraction (AF) increased from similar to 0.25 to similar to 0.48 in MgB2 made with purified B. These results demonstrate that intergranular MgO is an important current barrier in MgB2 and that it can be significantly reduced by boron purification.