Observation of strong to Josephson-coupled crossover in 10 degrees YBa2Cu3Ox bicrystal junctions

A temperature-dependent strong to weak (Josephson) coupling crossover near 75 K is observed for 10 degrees misorientation YBa2Cu3Ox grain boundaries. Below 75 K the current-voltage characteristic (IVC) shows strongly coupled, flux-flow behavior. Above 75 K, the IVC is Josephson coupled. The data are consistent with a network of microbridges at the grain boundary defined by dislocation strain fields. The data are compared to recent calculations by A. Gurevich and A. E. Pashitskii [Phys. Rev. B 57, 13878 (1998)]. The char acteristic voltages for these low-angle grain boundaries are higher than hi gh-angle boundaries at 77 K, and could lead to improved high-temperature su perconducting device operation in this temperature range. (C) 1999 American Institute of Physics. [S0003-6951(99)03046-6].