Effect of platinum addition on the microstructure and critical current density in (Nd,Eu,Gd)-Ba-Cu-O

We have studied the microstructure and magnetic properties of oxygen-contro lled-melt-growth (OCMG) processed (Nd, Eu, Gd)-Ba-Cu-O superconductors, whi ch contain about 40 mol% of (Nd, Eu, Gd)(2)BaCuO5 (NEG211) second phase by varying the amount of Pt from 0.25 to 3 mol%. Scanning electron and transmi ssion electron microscopic observations demonstrate that 0.5 mol% Pt is the optimum quantity to refine the 211 particles, leading to a dramatic increa se in the critical current density. An addition of 2-3 mol% Pt results in t he formation of relatively large NEG211 particles. J(c) values increase wit h increasing Pt content up to 0.5 mol% and then decrease thereafter. A high critical current density of 70 000 A cm(-2) at T = 77 K and an applied fie ld of 2.2 T (H parallel to c axis) is achieved in the sample with 0.5 mol% Pt. Our results demonstrate that the Pt addition is critical to the refinem ent of the 211 particle size and thus for the enhancement of the critical c urrent density.