Fabrication and properties of nano-CeO₂ doped YBCO bulk superconductors

Abstract

Single-domain Y–Ba–Cu–O (YBCO) bulk superconductors can be widely used in the superconducting maglev, cryomagnets, motors/generators fields. In order to improve the performance of the YBCO bulk superconductors further, in this article, nano-CeO₂ doped YBCO bulk superconductors were fabricated by two infiltration growth techniques (011-IG and 211-IG) respectively, in which two solid pellets of compositions Y₂O₃+1.15BaCuO₂+0.1CuO+1wt.% nano-CeO₂ and Y₂BaCuO₅ (Y-211)+1wt.% nano-CeO₂ were employed. And a novel pit-type seeding mode was used to prevent the movement of the film seed during the heat treatment process, then the growth morphology, microstructure and superconducting properties of the samples were investigated. The results show that, at low doping level (1wt.%), the normal growth of the YBCO crystal is not affected, and fully-grown single-domain YBCO bulk superconductors can be successfully prepared by the two techniques. Furthermore, the positions of the seeds have no any movement, which proves the effectiveness of the new seeding mode. The perpendicular growth sector boundaries on the top surface of the samples and clear (00l) series X-ray diffraction (XRD) peaks both prove the high c-axis orientation and high growth quality of the samples. The scanning electron microscopy (SEM) results indicate that, the nano-CeO₂ doping can effectively refine the size of the Y-211 micro-particles in the bulk superconductors, and this method is valid for both the two techniques. Low-temperature magnetization measurement shows that, the nano-CeO₂ doped sample prepared by the 011-IG method displays obviously superior <i>J</i>_c property than the undoped sample at low fields, which indicates that the refined Y-211 particles can effectively enhance the δ<i>l</i>-type pinning. In addition, compared with the 211-IG-processed sample, the 011-IG-processed sample performs better in the aspects of levitation force, microstructure and <i>J</i>_c property, thus the 011-IG method is a more promising preparation process. The results of this study are important for increasing the performance of the YBCO bulk superconductors as well as optimizing the fabrication technique further.