HOMOGENEITY OF TOP-SEEDED SINGLE-GRAINED YBCO SUPERCONDUCTORS

The homogeneity of J(c)(H,T) and microstructure of top-seeded melt-tex tured (TSMT) YBCO samples has been investigated systematically. A seri es of ten samples was cut from one single-grain sample at different di stances and orientations from the seed. SQUID magnetization measuremen ts of these ten samples have shown that J(c)(0 T, 75 K) varied from 1. 02 x 10(4) to 2.49 x 10(4) A m(-2) with an average of 1.80 +/- 0.45 x 10(4) A cm(-2). A second TSMT sample was sliced into four single-grain ed samples parallel to the a-b plane and the distribution of trapped m agnetic field mapped for each slice. The sample 3-6 mm below the seed exhibits the largest single peak with the highest trapped field. For s amples far away from the seed, very complicate patterns and various fi eld intensities were observed. It is believed that inhomogeneities wit hin the single-grained region of the sample may account for reports th at TSMT samples larger than about 3 cm diameter do not exhibit further improvements in their trapped magnetic field and associated levitatio n force. (C) 1998 Elsevier Science S.A. All rights reserved.