The development of melt-processed (Sm, Eu, Gd)Ba₂Cu ₃O_7-δ single-domain superconductors for high field applications

(Sm, Eu, Gd)Ba₂Cu₃O_7-δ (RE123) single-domain superconductors were grown in 1% O₂ in Ar with a modified hot-seeding melt process. Spatial superconducting variation and a local RE-Ba modulation were suppressed with the control of processing conditions. Pre-annealing at 960°C for 10 h in Ar prior to melt growth was found to significantly lower the range of RE-Ba substitution and diminish the number of pores and microcracks. Excess BaCuO_2-x was added to induce a Ba-enriched liquid and thereby hinder the nucleation of RE_1+xBa _2-xCu₃O_7-δ solid solution (RE123ss). The proper ratio of BaCuO_2-x to RE123 was around (0.17-0.25):1. The optimal thermal schedule was a fast cooling with a rate of 2°C h _-1 for 10 h followed by a 100 h slow cooling of 0.15°C h ^-1. A field of 1 T was trapped in a pellet of 35 mm diameter at 77 K and 2 T, which corresponded to the maximum external flux density of 3 T including the bias applied field.