A detailed comparison of the composition of (RE)-Ba-Cu-O-Ag bulk superconductors

Abstract

The homogeneity of the microstructure and composition are critical in determining the properties of rare earth-barium-cuprate, single grain bulk superconductors [(RE)BCO]. The magnitude of the trapped magnetic field achieveable in these technologically important materials, in particular, is influenced heavily by the size and distribution of (RE)₂BaCuO_x (RE-211) flux pinning inclusions in the bulk microstructure, whereas the size and distribution of silver agglomerates present within the bulk superconducting matrix correlate directly with improved mechanical properties. With careful engineering, these materials have significant potential for application in range of devices related to energy storage, medicine, electro-magnetic machinery and microelectronic technology. Fabrication of (RE)BCO bulk superconductors typically involves heating a powder compact above its peritectic decomposition temperature followed by slow cooling to facilitate the growth of a single grain. Each (RE)BCO composition has a different peritectic temperature and growth rate, which, therefore, necessitates different requirements in the heating profile. The fabrication temperature and growth rate, for example, may have an effect on the RE-211 and silver distribution, which may, in turn, affect the superconducting properties of the resulting single grain.

In this work we compare the distributions of silver and RE-211 in the single grain microstructures of YBCO-Ag, GdBCO-Ag, EuBCO-Ag and SmBCO-Ag bulk superconductors using optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. We observe that the distributions are very similar along both the a/b-axis and c-axis of these materials. This suggests that factors other than the maximum temperature used to achieve peritectic decomposition and the rate of single grain growth are particularly influential in determining the properties of the as-processed samples in the top seeded melt growth process. This observation demonstrates there is freedom to use (RE) materials interchangeably between different applications as required, for example, for functional or economic reasons.