34 Ë 2 Superconducting materials
Fig. 2.4:Single- and multi-seeded melt-textured HTS YBCO bulks (Adelwitz Technologiezentrum
GmbH (ATZ), Germany) [101].
In order to obtain a large single-grain bulk, Morita et al. [104, 105] in Nippon Steel
Corporation (NSC) succeeded in developing the RE compositional gradient technique
and prepared large-grained YBCO bulk superconductors with highJcvalues. Since
then, the research and development of HTS bulks has made steady progress [106].
Nippon Steel Corporation reported fabrication of large single-grained REBCO bulk
superconductors 150 mm in diameter using the RE compositional gradient technique.
Figure 2.5 shows a single-grain, 150 mm in diameter GdBCO bulk with a compositional
gradient of Dy. The insert in Fig. 2.5 is the trapped field distribution at 87 K, indicating
that the sample is a single-grain bulk with no serious weak links.
Another important superconducting characteristic of the melt textured YBCO
samples for the application is trapping flux. The magnitude of the trapped flux of
REBCO HTS bulks is proportional to its critical current densityJcand the volume. Krab-
bes et al. [107] prepared a cylindrical YBCO bulk with a modified melt crystallization
process (MMCP) [108]. A maximum field of 16 T was trapped at 24 K in the gap of a
Fig. 2.5:REBCO large single-grain bulk 150 mm in diameter fabricated (Nippon Steel
Corporation) [106].