Flux Pinning by BaCeO3 Nanoparticles in Single-Grain YBCO Superconductors

Abstract

The current study explores the effect of adding BaCeO₃ nanoparticles to Y-Ba-Cu-O (YBCO) composites, synthesized by the infiltration and growth process (IGP). BaCeO₃ nanoparticles synthesized using a wet-chemical method are added in two ways: directly to Y₂BaCuO₅ (Y-211) preform (set A) and indirectly through infiltrated liquid phase by adding to the YBa₂Cu₃O_7-δ (Y-123) source pellet (set B). The sol-casting technique was used for the uniform distribution of nanoparticles in the precursor powders by polymerization. Further processing of the preform pellets of composites by IGP led to single-grain growth in the composites, except at the highest (1 wt.%) BaCeO₃ content (x) in set A. It has been observed through detailed magnetization and microstructural studies that the addition of BaCeO₃ nanoparticles enabled interesting effects on the flux pinning landscape within the material. A systematic reduction in Y-211 particle size in both cases (sets A and B) indicates that BaCeO₃ nanoparticles react and refine the Y-211 phase significantly. Fishtail effect was observed at moderate concentrations and the optimum content of 0.5 wt.% BaCeO₃ addition enabled to achieve best critical current density and pinning force density at two studied temperatures of 50 and 77 K. Performance observed at x = 1 wt.% BaCeO₃ addition in set B is similar to that of 0.5 wt.% sample in set A. This shows that the properties are generally governed by the final BaCeO₃ content present in the YBCO matrix. A study of flux pinning mechanisms suggests point pinning at low x, whereas δk pinning is operative at medium x, where the fishtail effect is observed. Higher concentrations (1 wt.%) limited the single-grain growth, leading to a very broad diamagnetic transition and deteriorated the superconducting properties within the samples.