Fabrication of a good-quality single grain YBCO sample through the control of seed crystals

We investigated the growth mode of YBa/sub 2/Cu/sub 3/O/sub 7-y/ (Y123) grains and its effect on the levitation forces and trapped magnetic field of top-seeded melt processed YBCO samples. When a slab-like Sm-seed was used, undesirable subsidiary Y123 grains were formed, while the formation of the subsidiary Y123 grains was suppressed and a nearly single Y123 grain grew when a thick and wide seed was used. The formation of the subsidiary Y123 grains decreased the levitation forces and trapped magnetic field, due to the presence of grain boundaries with weak link characteristics.