Plates of melt-textured YBa₂Cu₃O_7-x superconductors with long crystals

Melt-textured plates of YBa₂Cu₃O_7-x measuring 400×(15-21)×(2.5-3.5) mm³ have been manufactured. They are composed of crystal bundles whose crystal size can be varied from some mm to more than 100×10×2.5 mm³ and recently up to 300×(5- 10)×3 mm³ depending on the process parameters. The crystals contain the usual Y₂BaCuO₅ inclusions, (001) microcracking and twinning. An unusual feature is the presence of continuous transitions between slightly misorientated subgrains or domains. The current-carrying capabilities of the samples have been tested by direct and alternating current measurements up to 1650 A_DC with current densities of 3600 A/cm² at 4 μV/cm (77 K). Magnetic characterization indicates low field critical current densities of the order of 10⁵ A/cm² at 77 K in small monocrystalline samples characterized by weakly developed (001) microcracking. Apparently appreciable flux flow occurs along defects in the long polycrystalline samples and the effective cross-section of these may be reduced due to microcracking. The plates are intended for relatively short current connectors, and could be used for current limiters where the very low voltage can be accepted. Relations between the microtextual features and the orientation dependence of the magnetic hysteresis have further been studied in the field range up to 1 T.