Superconducting properties of Dy-Ba-Cu-O bulk superconductors

We report on the superconducting properties of melt-textured Dy 123 bulk superconductors containing 5 to 40 mol% Dy211. Dy-Ba-Cu-O bulk samples were fabricated with the cold-seeding method in air using a Nd123 seed crystal. The superconducting properties of the bulk samples were strongly affected by the Dy211 content and the oxygen-annealing temperature. In the J_c-B curve of the Dy123 sample with 5 mol% of Dy211, the secondary peak was clearly observed at the applied fields of 0.5-2.0 T. The peak J_c values were 32 000-37 000 A cm^-2 at 77 K. The peak position shifted to lower fields with increasing oxygen-annealing temperature, presumably due to an increase in oxygen vacancies. We believe that the peak effect in Dy-Ba-Cu-O is ascribed to oxygen deficiency, since RE/Ba substitution is not present in the system. This idea was supported by the fact that the secondary peak decreased with increasing Dy211 contents and disappeared in the Dy123 sample with 40 mol% of Dy211.