Low-angle grain boundaries in YBa₂Cu₃O _7-δ with high critical current densities

The grain-boundary network in high-T_c coated conductors consists of a large number of low-angle grain boundaries with many types of misorientation. Using the bicrystal technology we have measured the critical current densities of the relevant YBa₂Cu₃O _7-δ grain boundaries as a function of the grain-boundary angle. We find that in the low-angle regime [010]-tilt boundaries and [100]-twist boundaries reduce the critical current density much less than [001]-tilt boundaries. Transmission electron microscopy reveals a low defect density in the [010]-tilt boundaries and we find that CuO₂ planes cross these boundaries without interruption.