Positive influence of ta addition on superconductive properties of high pressure synthesized MgB_2

TL;DR

This study demonstrates that adding tantalum during high-pressure synthesis enhances MgB2's superconductive properties by reducing impurities and forming beneficial compounds, resulting in high critical current densities and increased hardness.

Contribution

It reveals that tantalum addition improves MgB2 superconductivity and hardness by acting as an impurity getter during high-pressure synthesis, a novel approach for material enhancement.

Findings

Critical current densities of 570 kA/cm^2 at 10 K in 1 T

Vickers microhardness of MgB2 crystals exceeds sapphire hardness

Tantalum reduces impurity gases and promotes cleaner MgB2 formation

Abstract

Bulk MgB2 - based materials with the following critical current densities (jc) in 1 T field: 570 kA/cm^2 at 10 K, 350 kA/cm^2 at 20 K and 40 kA/cm^2 at 30 K and in 10 T field: 650 A/cm^2 at 10 K have been high-pressure (HP) synthesized from Mg and B with 2 - 10 wt.% addition of Ta. In synthesis and sintering process Ta plays the role of an absorbent of impurity gases (hydrogen, nitrogen, etc.) and forms Ta2H, TaH, TaN0.1, etc., thus promotes the reduction of MgH2 in Mg-B-O-matrix phase, as well as, the impurity nitrogen and oxygen in Mg-B grains (black MgB2 single crystals distributed over the matrix). Vickers microhardness of HP-synthesized material is Hv=12.54 (+/-)0.86 GPa (at 0.496-N load) The hardness (at 60-mN load) of MgB2 single crystals located in a sample matrix is 35.6 (+/-)0.9 GPa that is higher than the hardness of sapphire (31.1 (+/-)2.0 GPa).