The effect of seed orientation and separation on the field trapping properties of multi-seeded, melt processed Y–Ba–Cu–O

The size of large, individual bulk Y–Ba–Cu–O (YBCO) grains fabricated by top seeded melt growth (TSMG) determines fundamentally both the sample growth time and the homogeneity of microstructure more distant from the seed. Multiple seeds have been used in the TSMG process with their ab planes aligned to provide controlled multiple nucleation sites to promote grain orientation and improve the bulk microstructure. This study reports the influence of the angle of intersection of ab plane growth sector boundaries on trapped field and compares the results with those obtained for samples fabricated from perfectly-aligned seeds. The trapped field profiles on the surface of YBCO multi-seeded samples were measured using scanning Hall probe apparatus, and their microstructure investigated using high-resolution optical microscopy. It was observed that the homogeneity of adjacent, multi-seeded grains is related to the angle between the intersecting ab planes, with larger angles of mis-orientation producing significant minima in the trapped field profile. This suggests that the grain boundaries form weak links to the flow of current in multi-seeded samples. A single inverted parabolic flux profile, on the other hand, was observed for large grains fabricated from perfectly-aligned seeds. This preliminary study demonstrates the feasibility of fabricating strongly-coupled multiple grains by a multi-seeding technique and identifies seed alignment as a key parameter in achieving this processing aim.