Optimisation of the processing parameters for the fabrication of high-quality joints between Y–Ba–Cu–O single grain, bulk superconductors

Abstract

High-strength permanent magnets are essential for a wide range of technologies, including levitation devices, motors, generators and magnetic separators. Replacing permanent magnets with single grain, bulk superconductors will enable a step-change in the performance of these technologies by providing an order-of-magnitude increase in magnetic field. However, there remain many key challenges to the practical implementation of bulk superconductors, of which size and geometry are the most fundamental. The current limits to the size and geometry of (RE)-Ba-Cu-O single grain, bulk superconductors would be overcome substantially by the ability to fabricate high-quality joints between these technologically important materials. In this work we present new insights into the creation of superconducting joints between single grain bulk YBCO superconductors using a YBCO-Ag intermediate composition. We have investigated the effect of the joint fabrication temperature on the quality of the joint in order to begin to optimise the joint fabrication route for YBCO. We report on thirty five joints produced at different joining temperatures as part of this study. The trapped field properties of the resulting joined samples were measured and the microstructure at each joint was examined. We show that this simple and rapid joining technique is robust to small changes in joint fabrication temperature and suggest routes to further optimise this potentially transformative technique.