Processing and properties of large grain (RE)BCO

The potential of high temperature superconductors to generate large magnetic fields and to carry current with low power dissipation at 77 K is particularly attractive for a variety of permanent magnet applications. As a result large grain bulk (RE)-Ba-Cu-O ((RE)BCO) materials have been developed by melt process techniques in an attempt to fabricate practical materials for use in high field devices. This review outlines the current state of the art in this field of processing, including seeding requirements for the controlled fabrication of these materials, the origin of striking growth features such as the formation of a facet plane around the seed, platelet boundaries and (RE)(2)BaCuO5 (RE-211) inclusions in the seeded melt grown microstructure. An observed variation in critical current density in large grain (RE)BCO samples is accounted for by Sm contamination of the material in the vicinity of the seed and with the development of a non-uniform growth morphology at approximate to 4 mm from the seed position. (RE)Ba2Cu3O7-delta (RE-123) dendrites are observed to form and broaden preferentially within the alb plane of the lattice in this growth regime. Finally, trapped fields in excess of 3 T have been reported in irradiated U-doped YBCO and (RE)(1+x)Ba2-xCu3Oy (RE = Sm, Nd) materials have been observed to carry transport current in fields of up to 10 T at 77 K. This underlines the potential of bulk (RE)BCO materials for practical permanent magnet type applications. (C) 1998 Elsevier Science S.A. All rights reserved.