Degradation of Porosity and Enhanced Critical Current Density in MgB<sub>2</sub> with a Toluene-Treatment Boron Powder

Abstract

A series of MgB2 bulks with different porosity have been successfully prepared by in-situ solid-state reaction at ambient pressure with a toluene-treatment boron powder. The mass density reaches 1.86 g cm-3 at the most compact MgB2 bulk, which has an imporous microstructure, excellent grains coupling, clean grain boundaries and nanosized grains (100~200 nm). Our results reveal that the porosity of MgB2 can be significantly depressed by tuning the residual toluene content and heat treatment temperature in this way. Due to the degradation of porosity and thus the enhancement on grains connectivity and grains boundary pinning, the critical current density, Jc and irreversible fields Birr of MgB2 are significantly improved. For the best sample, at 20K, 4T and 10K, 6T, the Jc reach 2400 and 3700 A cm-2, which is higher than normal porous sample by a factor of 20 and 8, respectively; and the Birr at 20 K reaches 5.10 T.