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

Abstract

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.

Exploration of the Effect of Oxygen on Superconductivity in MgB2 Bulk by Using Boron Powder with Different Particle and Purification

“…As shown in the previous research [16], it is thought that the oxygen was embedded inside the B powder, which could not be eliminated. In this study, we tried to grind the B powder to decrease the particle size, which can expose more oxygen inside the powder.…”

“…The oxygen in the B powder could not be eliminated. Based on our analysis, as shown in Figure 10 from Reference [16], when a small B particle agglomerates to a larger one, the oxygen inside the large particles cannot be purified.…”

“…The purification process is described in our previous report [16]. Briefly, the B powder was treated by the high temperature and chemical solution.…”

“…To explore the effect of particle size, for the sample with grinding, the B powder was manually ground in an agate mortar for 0.5 h and then purified by the aforementioned methods. Only the best-purified B powder and Raw B powder were used to synthesize MgB 2 bulk using the same process as our previous report [16].…”

“…Since then, few researchers have purified B powder in order to eliminate the oxygen [12,14,15]. In 2019, we reported a systematical investigation on the purification of B powder by both heat treatment and chemical methods [16]. At that time, we found the heat treatment method to be more effective than the chemical method; however, both methods had limitations.…”