Effects of B₄C doping on critical current properties of MgB₂superconductor

Abstract

The relationships between microstructures, crystallinity and critical current properties for B4C doped MgB2 bulks, MgB2−5x(B4C)x with x = 0, 0.04, 0.1, 0.2 and 0.4, were systematically studied. Decreases of Tc and the a-axis length and deterioration of the crystallinity of MgB2 due to the carbon substitution occurred upon B4C doping. Substantially improved Jc was observed in the B4C doped MgB2 bulks especially at 5 K under high magnetic fields. Strengthened flux pinning at grain boundaries by carbon substitution was considered to contribute to the improvement of Jc. Furthermore, the reactivity of B4C with magnesium and boron was found to be much higher than that of graphite. These findings suggested that B4C is a promising carbon source dopant for MgB2 materials with excellent Jc properties, particularly under magnetic fields.