Progress in Buffer-Supported Seeding Architectures for Reliable Epitaxial Growth of REBa₂Cu₃O_7−δ Bulk Cryomagnets with Superior Properties

Abstract

Large-scale REBa2Cu3O7−δ (REBCO, RE = rare earth elements) superconducting crystals, whose excellent electromagnetic properties have been discovered over 30 years, possess considerable potential for scientific research and engineering applications. However, further development of these materials has been hindered by the lack of reliable fabrication processes. The controlled nucleation and growth of REBCO bulk cryomagnets for obtaining high crystallographic orientation and superior superconducting performance are strongly dependent on the seeding technique, including seed material, seeding architecture and seeding mode. In the most recent decade, a buffer layer technology has been developed for the growth of REBCO single grains, greatly enhancing the effectiveness of seeds. An overview of the most recent progress in seeding technology is presented by highlighting the advanced buffer-assisted seeding architectures. Distinctive functions of buffers are summarized as blocking the mutual contamination between the seed and the main pellet, enhancing seeding thermal stability by a seed/buffer layer structure and improving the bulk crystallinity as a larger secondary homoseed. The presented strategy gives valuable insight into the underlying mechanisms and provides tools for the seeding structural design in the growth of REBCO superconductors, which is scalable and can be extended to more functional oxide systems.