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

Single domain Y–Ba–Cu–O (YBCO) composed of a YBa2Cu3Oy (Y-123) superconducting bulk matrix with discrete, non-superconducting Y2BaCuO5 (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 in the 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 by conventional melt processing, which increases significantly with increasing sample diameter. Furthermore, samples grown by the IG technique exhibit low porosity of typically 0.9% of the bulk volume fraction, compared with a corresponding value of around 4.9% observed in samples fabricated by conventional melt processing. Fine Y-211 particles were observed to be embedded within the Y-123 superconducting matrix for the IG processed samples, leading to a high critical current density, Jc, of over 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 distribution of Jc. The volume fraction of Y-211 in the vicinity of the seed crystal (i.e. corresponding to the initial c-sector growth stage), in particular, is typically around 5%, compared with a value of up to 30% in the a growth sectors more distant from the seed crystal (which corresponds well to the theoretical value for the sample composition studied here). The volume fraction of Y-211 inclusions in the c growth sector more distant from the seed was around 22%. Finally, a trend of the variation in the distribution of Y-211 particles in the Y-123 matrix grown by the IG technique was similar to that in sample grown by conventional melt processing.