ABSENCE OF WEAK-LINK BEHAVIOR IN YBA2CU3O7 GRAINS CONNECTED BY 90-DEGREES [010] TWIST BOUNDARIES

ONE of the obstacles to developing applications of the high-T(c) copper oxide superconductors is the low critical current density (J(c)) of the bulk polycrystalline materials, due to the presence of grain boundaries. On the other hand, these same grain boundaries can be put to good use in device applications, where their low J(c) allows them to be used as 'weak links' in Josephson junctions 1,2. Dimos et al. 3,4 have shown that the transport properties of certain twist and tilt boundaries degrade as the misorientation angle increases, suggesting that high-angle grain boundaries are generally deleterious to the overall J(c). More recently, however, Babcock et al. 5 reported weak-link-free behaviour at high magnetic field in an YBa2Cu3O7-delta (YBCO) bicrystal containing two kinds of 90-degrees boundary; they were not able to distinguish between the characteristics of the two types, which were electrically in parallel. Here we report the observation of 90-degrees [010] twist boundaries in {103}-oriented YBCO thin films. (Because of the twin microstructure, we do not distinguish between the a and b axes). Across these boundaries the J(c) and normal-state conductivity are as high as those of high-quality c-axis-oriented films with no high-angle grain boundaries.