Effects of Gd₂BaCuO₅ addition on critical current characteristics in melt-processed (Nd, Eu, Gd)-Ba-Cu-O

We have investigated the effects of Gd₂BaCuO₅ (Gd21l) addition on the microstructure and J_c-B properties of oxygen-controlled-melt-growth (OCMG)-processed (Nd, Eu, Gd)-Ba-Cu-O system with scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and magnetization measurements. Compositional analyses revealed that small RE₂BaCuO₅ (RE211; RE: rare earth elements) particles consist mainly of Gd in the RE site, while large RE211 particles contain Nd, Eu and Gd despite the fact that only Gd211 was added to the system. Both zero field and peak J_c increased with increasing Gd211 content; however, J_c values were decreased when the amount of Gd211 reached 40 mol%. The sample (Nd, Eu, Gd)Ba₂Cu₃O_y added with 30 mol% of second phase Gd211 showed respective critical current densities of 71 000 and 52 000 A/cm² in O T and 2.6 T at 77 K for fields parallel to the c-axis. These results indicate that Gd211 addition to (Nd, Eu, Gd)-Ba-Cu-O is effective in improving J_c values through fine dispersion of Gd211.