Strong influence of boron precursor powder on the critical current density of MgB2

TL;DR

The study demonstrates that the type of boron precursor significantly affects the critical current density of MgB2 superconductors, with amorphous boron yielding substantially higher Jc than crystalline boron due to fewer Mg-B-O phases.

Contribution

This work reveals the strong influence of boron precursor nature on MgB2's superconducting properties and proposes mechanisms for the observed differences.

Findings

Amorphous boron leads to at least three times higher Jc than standard samples.

Crystalline boron results in about an order of magnitude lower Jc due to Mg-B-O phases.

Fewer Mg-B-O phases are present in amorphous B samples despite higher B2O3 content.

Abstract

The influence of the nature of the boron precursor on the superconducting properties of polycrystalline MgB2 was studied. Critical current densities for the MgB2 made from high purity amorphous boron are at least a factor of three higher than typical values measured for standard MgB2 samples made from amorphous precursors. Two possible mechanisms are proposed to account for this difference. Samples made from crystalline boron powders have around an order of magnitude lower Jc compared to those made from amorphous precursors. X-ray, Tc and resistivity studies indicate that this is as a result of reduced current cross section due to the formation of Mg-B-O phases. The samples made from amorphous B contain far fewer Mg-B-O phases than crystalline B despite the fact that the amorphous B contains more B2O3. The different reactivity rates of the precursor powders accounts for this anomaly.