High-temperature-superconductor coated conductors: technical progress in Japan

It is now a widespread view that a high-Jc superconducting wire with a high performance under strong magnetic fields at liquid-nitrogen temperature needs to be realized by the material Y-123. However, because of the weak linking nature of this material, the fabrication of the wire must be based on a coated-conductor process to achieve a highly textured Y-123 thin film on a long starting wire tape. Various attempts to obtain a textured substrate with sizable length have been made by various methods, with or without the aid of buffer layers. Approaches to the fabrication of an epitaxial thin film of Y-123 have also been made from vapour, liquid, or solid phases by different methods. Therefore, combinations of these proposed processes in each category have led to several promising on-going worldwide approaches to achieve the realization of practical coated superconducting wires in the near future. This review focuses on the most outstanding achievements in Japan.