Strong pinning in ternary (Nd-Sm-Gd)Ba₂Cu₃O _y superconductors

We have studied the flux pinning in melt-textured (Nd_0.33Sm _0.33Gd_0.33)Ba₂Cu₃O_y NSG-123 superconductors with various numbers of Gd₂BaCuO₅ (Gd-211) particles. Transmission electron microscopy (TEM) showed that submicron Gd-211 particles are uniformly distributed in the superconductive matrix. Dark-field TEM observations further showed that a high density of RE rich RE_1+xBa_2-xCu₃O_y (RE-123ss) clusters 3-10 nm in size were distributed in the NSG-123 matrix. A strongly developed fishtail was observed in the magnetization hysteresis loops of all the samples. A critical current density of 100 kA/cm² (77 K) was achieved at the secondary peak field of 2 T for the H∥c axis in the NSG-123 sample with 10 mol% Gd-211. Large grain NSG-123 pellets with 30 mol% Gd-211 and 20 wt% AgO ₂, 30 mm in diameter and 15 mm in height, exhibited a single-cone profile with a peak value of 1.2 T at 77 K. A higher trapped-field value of 1.5 T was recorded at 2 T, reflecting the secondary peak effect.