Dislocation structure of low-angle grain boundaries in YBa2Cu3O7-delta/MgOfilms

Grain boundaries in laser-deposited YBa2Cu3O7-delta (YBCO)/MgO thin films h ave been investigated by high-resolution transmission electron microscopy. The films exhibit perfect texturing with YBCO(001)/MgO(001) giving rise to low-angle [001] tilt grain boundaries resulting from the grains with the c axis normal to the substrate surface and with misorientation in the a-b pla ne. The atomic structure of the grain boundaries was analyzed by using a di slocation model, Low-angle grain boundaries have been found to be aligned a long (100) and (110) interface planes. For the (110) boundary plane, the lo w-energy dislocation configuration was found to consist of an array of alte rnating [100] and [010] dislocations, We have calculated the energy of vari ous configurations and shown that the energy of the (110) boundary with dis sociated dislocations is comparable to that of the (100) boundary, which ex plains the coexistence of (100) and (110) interface facets along the bounda ry. We have also modeled critical current transport through grain boundarie s with various structures and found that the low-energy (110) grain boundar y with dissociated dislocation array is expected to transport a lower super conducting current (by 25% for 6 degrees misorientation) than (100) boundar ies.