Solidification path of YxNd1-x+yBa2-yCu3O6+δ superconducting composites

The formation of YxNd1-x+yBa2-yCu3O6+delta solid solution ((Y, Nd) 123ss) has been investigated under air and 0.1% oxygen partial pressure by an in situ top-seeded melt-growth technique. It is found that both Nd/Y and RE/Ba substitutions occur in (Y, Nd) 123ss crystals grown under air, in which the Y and Ba concentrations increase as solidification proceeds. In crystals grown in reduced pO(2), on the other hand, the Nd/Ba substitution is suppressed significantly although Nd is observed to substitute onto the Y site. These variations of substitution during solidification can be explained qualitatively using the quasi-ternary phase diagram, in a similar manner to the Nd/Ba solid solution formation that occurs in undoped Nd 123. Another important observation is that the size of secondary particles, stable at high temperature, decreases dramatically in this material compared with those in Nd 123. In addition, no significant influence of Y/Nd substitution on the T-c of (Y, Nd)123ss is observed, in contrast to an abrupt decrease in T-c associated with the Nd/Ba substitution in undoped Nd123. As a result, (Y, Nd)123ss crystals grown under reduced pO(2) exhibit significantly enhanced J(c) compared to Nd 123 over a wide range of applied magnetic fields at lower temperatures (approximate to 50 K).