Seeded infiltration and growth of large, single domain Y–Ba–Cu–O bulk superconductorswith very high critical current densities

Abstract

Single domain Y–Ba–Cu–O (YBCO) composed of aYBa2Cu3Oy (Y-123) superconducting bulk matrix with discrete, non-superconductingY2BaCuO5 (Y-211) phase inclusions has been fabricated by a seeded infiltration and growth (IG)technique in the form of cylindrical pellets up to 32 mm in diameter. Sample shrinkage inthe radial direction for single domains prepared by this technique is relatively low at 5%and independent of sample size, in contrast to the shrinkage observed in samples grown byconventional melt processing, which increases significantly with increasing samplediameter. Furthermore, samples grown by the IG technique exhibit low porosity oftypically 0.9% of the bulk volume fraction, compared with a corresponding value ofaround 4.9% observed in samples fabricated by conventional melt processing. FineY-211 particles were observed to be embedded within the Y-123 superconductingmatrix for the IG processed samples, leading to a high critical current density,Jc, ofover 100 000 A cm−2 at 77.3 K in self-field. The distribution of Y-211 particles in the IG sample microstructure, however,was inhomogeneous (unlike in previous reports), which leads to a variation in the spatial distributionof Jc. The volume fraction of Y-211 in the vicinity of the seed crystal (i.e. corresponding to the initialc-sector growth stage), in particular, is typically around 5%, compared with a value of up to 30% inthe a growth sectors more distant from the seed crystal (which corresponds well to the theoreticalvalue for the sample composition studied here). The volume fraction of Y-211 inclusions in thec growth sector more distant from the seed was around 22%. Finally, a trend of thevariation in the distribution of Y-211 particles in the Y-123 matrix grown by the IGtechnique was similar to that in sample grown by conventional melt processing.