Strong Flux Pinning In Melt-Grown RE123 (RE: Sm, Eu, Gd) Superconductors

REBa2Cu3Oy superconductors with rare earth (RE) ions with large radii (RE: La, Nd, Sm, Eu) 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 YBa2Cu3Oy 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(Ba1−x,REx)2Cu3Oy phase in a good superconductive matrix.