A novel interior seed addition to improve the levitation force and the trapped field of multi-seeded YBCO bulk superconductors

Top multi-seeded technique (TMS) is a cost-effective and time-saving method in fabricating larger size high-quality REBCO bulk superconductors. However, the physical properties of the samples prepared by the TMS technique are clearly reduced compared to the single domain samples, especially around the grain boundaries between the neighboring grains. Here we have proposed a novel Inner-Top Multiple-Seeding (IT-MS) technique, which can be used to design and optimize the shapes and space configuration of the single-domain YBCO grains, so as to improve the physical properties of multi-seeded REBCO bulk sample. These have been verified with 60 x 20 x 13 mm3 parallelepiped YBCO bulk superconductors. The levitation force of 112.8 N (77 K, 0.5 T) is achieved in the sample prepared by the IT-MS method with two top seeds and one interior seed, which is 25.2% and 16.9% higher than that of the samples prepared using the TMS method with only two and three top seeds. The trapped field of the IT-MS sample is not only higher than that of the TMS sample, but also the magnetic field coupling ratio is significantly enhanced from 44.2% to 65.1%. The results indicate that the IT-MS technique is helpful to improve the physical properties and homogeneities of the multi-seeded YBCO bulk samples, especially effective for the fabrication of high-quality larger size REBCO bulk superconductors.