Microstructure and flux pinning in oxygen-controlled melt-growth processed (Nd_0.33Eu_0.33Gd_0.33)Ba₂ Cu₃O_y

We fabricated single-domain (Nd_0.33Eu_0.33Gd_0.33)Ba₂ Cu₃O_y (NEG123) bulk superconductors with a top-seeded melt-growth process in Ar-0.1%O₂ atmosphere using melt-textured Nd-123 as a seed crystal. We added a variety of secondary phase particles ((Nd,Eu,Gd)211, (Eu,Gd)211, Eu211, Gd211) in different amounts to the NEG123. Scanning electron microscopy observations demonstrated that the morphology, the particle size, and the distribution were strongly dependent on the concentration and the type of secondary phase. In addition, the chemical analyses revealed that the matrix composition also changes with the secondary phase particles. They also strongly affected the critical current density (J_c) and the irreversibility fields. The self-field and peak J_c values will be discussed with relation to the type of pinning mechanisms.