THE ATOMIC ORIGINS OF REDUCED CRITICAL CURRENTS AT [001]-TILT GRAIN-BOUNDARIES IN YBA2CU3O7-DELTA THIN-FILMS

Grain boundaries have long been known to have a deleterious and irrepr oducible effect on the transport properties of high-T-c oxide supercon ductors, particularly in the high-angle regime where an exponential de crease 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 t hat dominates this behavior. [001] tilt grain boundaries in thin-film YBa2Cu3O7-delta are composed of arrays of dislocations in defined sequ ences, The resulting strain fields seriously perturb the local electro nic structure, leading to a non-superconducting zone at the grain boun dary. The width of this zone increases linearly with misorientation an gle, naturally explaining the observed exponential decrease in critica l current. In addition, the widely varying J(c) measurements for a giv en grain boundary misorientation can be naturally explained by the fac etting of the grain boundary plane. (C) 1998 Elsevier Science B.V.