Microstructure of superconducting hetero-joints between single-grained Gd-Ba-Cu-O bulk superconductors

A wide range of technologies rely on permanent magnets, including levitation devices, motors, generators and magnetic separators. Replacing permanent magnets with bulk superconductors will enable a step change in performance by providing an order of magnitude increase in the achievable magnetic field. However, the reliable fabrication of large single grained superconducting materials with a high, homogeneously distributed magnetic trapped field remains a barrier to the widespread application of these materials. Limits to the size and geometry of RE-Ba-Cu-O single grain bulk superconductors could be overcome by developing a reliable process to assemble larger components by fabricating superconducting joints between smaller samples. In this work we propose a mechanism of joint formation in GdBCO-Ag bulk superconductors using a YBCO-Ag intermediate that is based on detailed analysis of the joint interfaces. This improved understanding of the joint formation process provides the knowledge required to fully optimise the fabrication parameters, and to produce joints with improved superconducting and mechanical properties.