The atomic origins of reduced critical currents at [001] tilt grain boundaries in YBa2Cu3O7-δ thin films

Grain boundaries have long been known to have a deleterious and irreproducible effect on the transport properties of high-T-c oxide superconductors, particularly in the high-angle regime where an exponential decrease in critical current has been reported. We demonstrate, through a combination of atomic resolution Z-contrast imaging and bond valence sum analysis, that it is the atomic structure of the grain boundary that dominates this behavior. [001] tilt grain boundaries in thin-film YBa2Cu3O7-delta are composed of arrays of dislocations in defined sequences, The resulting strain fields seriously perturb the local electronic structure, leading to a non-superconducting zone at the grain boundary. The width of this zone increases linearly with misorientation angle, naturally explaining the observed exponential decrease in critical current. In addition, the widely varying J(c) measurements for a given grain boundary misorientation can be naturally explained by the facetting of the grain boundary plane. (C) 1998 Elsevier Science B.V.