Fabrication of high-quality joints between Gd-Ba-Cu-O bulk superconductors

Abstract

This work reports a technique for fabricating superconducting joints between GdBCO-Ag bulk superconductors, using YBCO-Ag as an intermediate joining material. The ability to provide reliable joints between multiple bulk superconductors overcomes many of the challenges of fabricating large superconductors or machining hard and brittle bulk superconductors into practical shapes. We report on nine single grains of GdBCO-Ag which have been joined with a YBCO-Ag intermediate. Samples were cut and joined in a variety of c-plane orientations to refine and understand the effect this had on the superconducting properties of jointed samples. The trapped field of pre-jointed and jointed bulk superconductors were compared; the maximum trapped field achieved was 59% of the pre-jointed sample. Further analysis showed that the critical temperature and critical current of the samples were degraded by the jointing process. Microstructural and chemical analysis showed that the jointing process facilitated diffusion of silver towards the joint and in some cases large pores were formed at the joint interface. These factors consequently inhibited current flow across the joint and thus reduced the maximum trapped field achievable when compared to the original unjointed sample.