Enhanced magnetic properties of YBa2Cu3O7−δ bulk superconductors with tailored structure by a novel seeding assembly

Abstract

YBa2Cu3O7−δ (YBCO) bulk superconductors are regarded as the most promising alternatives for conventional permanent magnets as they provide high field trapping capacity at low temperatures. However, for further improving their superconducting properties, it remains a significant challenge to enlarge the c growth sector by large-sized seeds or multi-seeds while maintaining the microstructure with a low porosity or clean grain boundaries that enables their performance. Here, we report a novel seeding assembly approach by vertically-connecting strip-seeds for inducing potential [110]-oriented overgrowth. Initially, from naturally right-angled corners, YBCO rapidly crystallized to form kite-liked convex areas, which, together with the original seed, effectively functioned as a large-sized seed to generate a sizable c growth sector. The novel-seeded sample exhibited a promising structure not only free of grain boundaries, but also with a favorable porosity of 20.29%. Such a low value is similar to 19.77% of the small-seeded one and much lower than 34.20% of the large-seeded one. Finally, due to structure tailoring towards an enlarged c growth sector with maintained pore characteristics, high and mono-peak trapped fields of 16 mm diameter YBCO bulks were reliably attained, up to a record value of 0.7025 T. This work offers insights into design principles for boosting magnetic properties of other members in the YBCO family.