Key Materials for Superconducting Devices

Dear Colleagues,

Much of the effort involved in superconducting innovation is centered on high-temperature superconductors (HTS) and, within this field, on REBa₂Cu₃O₇−δ (REBCO) compounds. These materials are the resources used for the preparation of second-generation (2G) high-Tc superconducting tapes, known as coated conductors (CCs), crucial for high-field magnets, motors, generators, and fault current limiters. The aim of this Special Issue is to optimize their performance while reducing production costs.

Traditional methods, like metal–organic chemical vapor deposition (MOCVD), pulsed laser deposition (PLD), and sputtering, have been the go-to options for REBCO films. However, chemical techniques, particularly chemical solution deposition (CSD), have emerged as cost-effective alternatives, enhancing film quality and cost efficiency.

Meanwhile, research continues to explore novel applications for low-temperature superconductors (LTS), which are currently practical only when immersed in a liquid helium bath. The high-energy physics community has recently rekindled interest in Nb₃Sn, particularly for the development of dipole and quadrupole magnets intended for the LHC upgrade (Hi-Lumi LHC) and the Future Circular Collider (FCC) at CERN.

Between these two extremes, other superconducting materials with intermediate T_C values exist that may have specialized applications. A prime example is MgB₂, already employed in magnetic resonance imaging (MRI) machines and previously tested for the creation of fault current limiters. With a T_c of approximately 40 K, it is suitable for applications in the 15–20 K range, achievable via cryocoolers or liquid hydrogen–neon environments.

Iron-based superconductors (IBS) are emerging as promising candidates for various applications. These materials include a wide number of phases with diverse crystal structures and T_Cs. What unites them is the presence of an active layer where iron is bonded to either arsenic or chalcogenides, such as selenium or tellurium. Owing to their exceptional in-field properties, several phases of IBS have demonstrated significant potential for future practical applications and device fabrication, operating across a wide temperature range, i.e., from 4.2 to 30 K.

This Special Issue of Crystals welcomes research papers presenting groundbreaking ideas and methods to further advance the knowledge of superconducting materials, superconductivity, superconductors, superconducting tapes, coils, and flux pumps, thus propelling superconducting devices into the future.

Dr. Pablo Cayado
Dr. Haitao Yang
Dr. Gianmarco Bovone
Guest Editors

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• superconductivity
• superconducting materials
• superconductors
• high temperature superconductors (HTS)
• REBCO
• superconducting tapes
• Nb₃Sn
• MgB₂
• low-temperature superconductors (LTS)
• iron-based superconductors (IBS)
• superconducting coils
• flux pumps