Hot isostatic pressing of powder in tube MgB2 wires

TL;DR

This study demonstrates that hot isostatic pressing significantly enhances the critical current density and magnetic properties of MgB2 wires by inducing structural defects that improve vortex pinning, making them more suitable for practical applications.

Contribution

It introduces hot isostatic pressing as a method to improve MgB2 wire performance by increasing defect density and vortex pinning capabilities.

Findings

HIPed wires have higher Jc than annealed wires, especially at high fields.

HIPed wires exhibit higher irreversibility fields (Hirr).

Structural defects observed include boundaries and sub-grains that enhance vortex pinning.

Abstract

The critical current density (Jc) of hot isostatic pressed (HIPed) MgB2 wires, measured by d.c. transport and magnetization, is compared with that of similar wires annealed at ambient pressure. The HIPed wires have a higher Jc than the annealed wires, especially at high temperatures and magnetic fields, and higher irreversibility field (Hirr). The HIPed wires are promising for applications, with Jc>106 A/cm2 at 5 K and zero field and >104 A/cm2 at 1.5 T and 26.5 K, and Hirr ~ 17 T at 4 K. The improvement is attributed to a high density of structural defects, which are the likely source of vortex pinning. These defects, observed by transmission electron microscopy, include small angle twisting, tilting, and bending boundaries, resulting in the formation of sub-grains within MgB2 crystallites.