Effect of Eu₂BaCuO₅ addition on the matrix composition and flux pinning in (Nd_0.33Eu_0.33Gd_0.33)Ba₂Cu₃O_y superconductors

We have investigated the microstructure and flux-pinning properties of the (Nd_0.33Eu_0.33Gd_0.33)Ba₂Cu₃O_y (NEG-123) bulk superconductors with the addition of different amounts of Eu₂BaCuO₅ (Eu-211) secondary phase particles using SEM, EPMA and magnetic measurements. The SEM study showed that the submicrometre secondary-phase particles were finely distributed in the NEG-123 matrix. Chemical analyses revealed that the matrix composition changed with the quantity of Eu-211 particles. The scaling study of the volume pinning forces showed that the peak position lies around h≈0.52, which indicates enhanced ΔT_c-type pinning. For the NEG-123 sample with 20 mol% Eu-211 additions, a large critical current density (J_c) of 50 000 A cm^-2 was achieved at 77 K and 2.7 T for the H∥c axis.