Systematic investigation into the effect of boron powder purified by different methods on the microstructures and superconductivity of MgB2 bulks

Commercial boron powder was purified by a heat treatment method and a chemical method, and the effect of the differently purified powders on the microstructure and superconductivity of MgB2 was systematically investigated. Both purification processes successfully decreased the oxygen content, but neither could completely eliminate oxygen in the boron powder. The significant degradation of MgO peaks and increase in superconductivity for the sample with heat treatment purified boron powder indicated the best purification performance. For comparison, MgB2 bulks with chemical purified boron powder were also investigated. The reason of incomplete purification on the oxygen and the reaction mechanisms for the differently purified boron powders during the synthesis of MgB2 were uncovered. This research provides an important foundation for understanding the reaction of oxygen during MgB2 synthesis, and thus finally reveals the effect of oxygen on superconductivity in this system.