Flux pinning in melt-grown NdBa₂Cu₃O_y and SmBa₂Cu₃O_y superconductors

REBa₂Cu₃O_y superconductors with rare earth (RE) ions with large radii (RE: La, Nd, Sm) exhibit relatively low T_c due to the presence of RE-Ba solid solution. We have found that this solid solution can be suppressed if these superconductors are melt processed in a reduced oxygen atmosphere. We have also found that critical current densities of these superconductors are higher than those of melt processed YBa₂Cu₃O_y with fine Y₂BaCuO₅ inclusions in a high field region. The irreversibility line was also shifted toward the higher H-T region. We believe that flux pinning in these superconductors is ascribable to a finely distributed RE(Ba_1–x, RE_x)₂Cu₃O_y phase in a good superconductive matrix.