Homogeneity of top-seeded single-grained YBCO superconductors

The homogeneity of Jc(H,T) and microstructure of top-seeded melt-textured (TSMT) YBCO samples has been investigated systematically. A series of ten samples was cut from one single-grain sample at different distances and orientations from the seed, SQUID magnetization measurements of these ten samples have shown that Jc(0 T, 75 K) varied from 1.02 × 104 to 2.49 × 104 A m−2 with an average of 1.80 ± 0.45 × 104 A cm−2. A second TSMT sample was sliced into four single-grained samples parallel to the a-b plane and the distribution of trapped magnetic field mapped for each slice. The sample 3–6 mm below the seed exhibits the largest single peak with the highest trapped field. For samples far away from the seed, very complicate patterns and various field intensities were observed. It is believed that inhomogeneities within the single-grained region of the sample may account for reports that TSMT samples larger than about 3 cm diameter do not exhibit further improvements in their trapped magnetic field and associated levitation force.