Flux Pinning in Melt-Grown NdBa₂Cu₃Oy and SmBa₂Cu₃Oy Superconductors

REBa 2 Cu 3 O 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 YBa 2 Cu 3 O y with fine Y 2 BaCuO 5 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 ) 2 Cu 3 O y phase in a good superconductive matrix.