Comparison of the Microstructure and Superconducting Properties of Eu-Ba-Cu-O and Gd-Ba-Cu-O Single Grain Samples

Bulk Rare Earth-Ba-Cuprate [(RE)BCO] superconductors fabricated in the form of large single grains consisting of a REBa2Cu3O7-delta (RE-123) matrix and RE2BaCuO5 (RE-211) inclusions can generate trapped magnetic fields that are up to ten times higher than the maximum fields obtainable in conventional Fe-based permanent magnets. The choice of the Rare Earth (RE) element plays a key role in determining the growth rate of single grains, the precise microstructure, mechanical properties and hence the final superconducting properties of the bulk samples, and also the likelihood of RE substitution onto the Ba site which can degrade the performance. In this work, we have studied the growth and microstructure of (RE)BCO single grains with RE = Gd and Eu, where the degree of Ba substitution is known to be very different. We have carried out detailed microstructural characterization of the phase distribution and composition using high resolution electron microscopy to understand the effects of Gd and Eu on the uniformity of the samples, the distribution of the secondary 211 phase, porosity and chemical variations in different regions of the melt-grown single grains.