Sheath and barrier materials in MgB ₂ conductors: structures, properties, and application-oriented selection strategies

Abstract Magnesium diboride (MgB 2 ) has emerged as a promising superconducting material for various technological applications, including magnetic resonance imaging (MRI), superconducting magnets, fault current limiters, and power transmission systems. While considerable progress has been made in the development of MgB 2 -based wires, tapes, and cables, the selection and optimization of sheath and barrier materials remain critical challenges that significantly influence the performance, stability, and manufacturability of these conductors. This review presents a comprehensive examination of the current state of sheath and barrier materials used in MgB 2 conductors. It discusses their functional roles, material requirements, and processing constraints, with particular emphasis on chemical compatibility, mechanical strength, thermal behaviour, and diffusion barrier effectiveness. Conventional sheath materials such as iron, copper, nickel, and stainless steels are evaluated alongside emerging advanced and composite systems. Similarly, barrier materials including niobium, tantalum, titanium, and ceramic coatings are analysed in terms of their ability to mitigate interfacial reactions and maintain conductor integrity under thermal processing. Comparative analysis of sheath–barrier systems and application-specific requirements are addressed in detail. Finally, the review identifies key challenges and outlines future directions for material innovation, including multilayer architectures and data-driven material selection strategies. The insights provided here aim to guide the rational design and engineering of high-performance MgB 2 conductors for next-generation superconducting technologies.