Manufacture of bulk superconducting YBa₂Cu₃O_7-δ by a continuous process

THE high critical current densities (J _cs) measured in thin films and within grains of the high-transition-temperature (high-MT_c) oxide superconductors indicate that low J _c should not prevent the use of high-T _c materials in high-current devices¹. Indeed, a J _c of ∼7.5×10⁴ A cm^-2 has been obtained in highly textured bulk YBa₂Cu₃O₇ ('123') at 0 T, processed by a melt-textured² or liquid-phase³ growth technique. Unfortunately, textured materials with this improved J _c comprised only a very small portion (< 1 cm) of the bulk precursor, which had random grain orientations on a larger scale. For high-current applications, one needs bulk materials fabricated in usable shapes of large dimensions with controlled grain orientation to carry a high total current, not just a high current density. Here we report the development of a continuous process for fabricating large bulk superconductors with a pre-determined grain orientation. A bar of the 123 compound with dimensions 5 x 0.5 x ∼0.3 cm with excellent grain alignment (a-b plane along the longest sample dimension) has been fabricated continuously. The bulk 123 thus obtained has magnetically determined J _cs of ∼3 x 10⁴ and 1.2 x 10⁴ A cm^-2 at 0 and 1 T, respectively and transport J _cs of 2 x 10⁴, 1.1 x 10⁴ and 7.5 x 10³ A cm² at 0, 0.54 and 0.83 T.