Anisotropic Crystallinity/Disorder and In-field Transport Performance of Multi-band MgB₂ Materials

Abstract

Multi-band MgB₂ materials have been considered and developed for medical and energy applications. Since some of these applications require kilometers-long wires or tapes, many companies have developed MgB₂ materials with fabrication processes through powder filling (e.g., a powder-in-tube process), which can satisfy the requirements of the long lengths for commercial production. These material structures have also been studied to enhance the transport performance of the critical current in magnetic fields. For in-field enhancement, it is essential to gain a deep understanding of crystallinity/disorder (which is related to grain growth, the number of defects, and the distribution of strain/distortion). The material crystallinity, which affects the in-field performance, can become anisotropic due to the structural nature of MgB₂, but most studies have not focused on this anisotropy. Therefore, this review highlights and discusses multi-band MgB₂ materials in terms of critical current performance and anisotropic crystallinity. This perspective can also be useful for further modifying the material structures of wires, tapes, bulks, powders, etc.