Disorder anisotropy of layered structure in multi-band MgB2 superconducting materials with high critical current performance

• Published in: Journal of alloys and compounds 2023-02, Vol.934, p.167873, Article 167873
• Main Authors: Maeda, Minoru, Choi, Jun Hyuk, Knott, Jonathan C., Kim, Jung Ho, Hahn, Garam, Kang, Hyoungku, Hahn, Seungyong, Choi, Seyong
• Format: Article
• Language: English
• Subjects: Anisotropy; Critical current density; Disorder; MgB2 wire; X-ray methods
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2022.167873

Layered crystal structures of various materials form through strong in-plane covalent and weaker out-of-plane bonding. The different bonding states can lead to the appearance of anisotropies not only of electronic/electrical and magnetic properties but also of structural disorder. A deeper understanding of the disorder anisotropy is essential to carry out structural modification and to enhance the material properties. However, in the case of multi-band MgB2 superconducting materials that have layered structures, including graphene-like and six-membered rings, the nature and extent of the disorder anisotropy are not well understood. Also unknown is the influence on the transport critical current performance under magnetic fields in terms of charge-carrier scattering and vortex pinning. Herein, we have investigated the disorder anisotropy to reveal the relation with the in-field superconductivity. The MgB2 phase formed by appropriate sintering conditions with carbon doping for high transport critical current performance exhibited a small anisotropy in the strain distribution and a large anisotropy in the crystallite size. The anisotropic behavior reflects small out-of-plane domains of crystallites with the strain distribution. The disordered formation may be the reason why the π band is usually dirtier than the σ band. In contrast, although the strain distribution in the in-plane structural state can be selectively tuned by carbon doping, the in-plane crystal growth is still considerably large. Such in-plane crystallization has shortcomings in terms of scattering and pinning. We therefore argue that further selective modification of the disordered structure, especially for the in-plane size properties, is a practical approach to achieve enhancement beyond the currently attainable transport performance. •The MgB2 superconductor has a layered structure, with dimensionally different and weakly interacting multiple bands.•By tuning the charge-carrier scattering for the bands, MgB2 still has room to further improve the electrical properties.•We elucidated the in-plane and out-of-plane disordered structures with the anisotropy in high-performance MgB2 materials.•The in-plane mean periodic distance was much larger than the in-plane superconducting coherence lengths in clean samples.