Seeded infiltration and growth of single-domain Gd–Ba–Cu–O bulk superconductors usinga generic seed crystal

Abstract

We report the seeded infiltration and growth (IG) of Gd–Ba–Cu–O (GdBCO) bulksuperconductors for varying molten Ba–Cu–O liquid compositions using an Mg-dopedNd–Ba–Cu–O (Mg-NdBCO) melt-textured seed crystal developed recently at the IRC. Allthe samples were grown in the form of single grains, although the size of the grain wasobserved to decrease for an increasingly Ba-rich initial composition. The size ofGd2BaCuO5 (Gd-211)particles in the GdBa2Cu3Oy (Gd-123) phase matrix is almost constant for samples with differentBaO2 content in the liquid source pellet. The volume fraction of Gd-211 in the Gd-123 matrix(Vf211), however, decreases significantly with increasingBaO2 content. The superconducting transition temperature,Tc,and transition width within the entire seeded IG bulk GdBCO grain are also extremely sensitive toBaO2 concentration. A maximum critical current density,Jc,of 88 000 A cm−2 at 77.3 K in self-field is observed in this study in the sample containing the greatest concentration ofBaO2 in the liquid source pellet grown in air and without further Ar and/orlow oxygen heat treatment (which would give further improvements inthe superconducting properties of the samples). The highest value ofJc observed inthis study of 115 000 A cm−2 at 77.3 K in self-field was obtained in the sample grown in a1% O2+N2 atmosphere. These results indicate that the seeded infiltration and growth techniqueproduces effective pinning centres in the bulk microstructure, at least in the self-field limit.