Towards the Realization of Higher Connectivity in MgB2 Conductors: In-situ or Sintered Ex-situ?

TL;DR

This study demonstrates that optimized sintering of ex-situ MgB2 conductors significantly enhances their electrical connectivity, surpassing traditional in-situ methods, by promoting self-sintering and improving microstructure.

Contribution

It reveals that self-sintering in ex-situ MgB2 can achieve higher connectivity than in-situ methods, offering a new pathway for better superconductor performance.

Findings

Sintered ex-situ MgB2 shows increased packing factor and lower resistivity.

Connectivity in sintered ex-situ MgB2 exceeds 15%, surpassing in-situ levels.

Self-sintering can potentially double the connectivity of ex-situ MgB2.

Abstract

The two most common types of MgB2 conductor fabrication technique - in-situ and ex-situ - show increasing conflicts concerning the connectivity, an effective current-carrying cross-sectional area. An in-situ reaction yields a strong intergrain coupling with a low packing factor, while an ex-situ process using pre-reacted MgB2 yields tightly packed grains, however, their coupling is much weaker. We studied the normal-state resistivity and microstructure of ex-situ MgB2 bulks synthesized with varied heating conditions under ambient pressure. The samples heated at moderately high temperatures of ~900{\deg}C for a long period showed an increased packing factor, a larger intergrain contact area and a significantly decreased resistivity, all of which indicate the solid-state self-sintering of MgB2. Consequently the connectivity of the sintered ex-situ samples exceeded the typical connectivity range 5-15% of the in-situ samples. Our results show self-sintering develops the superior connectivity potential of ex-situ MgB2, though its intergrain coupling is not yet fulfilled, to provide a strong possibility of twice or even much higher connectivity in optimally sintered ex-situ MgB2 than in in-situ MgB2.