Microstructure of an artificial grain boundary weak link in an YBa2Cu3O7−σ thin film grown on a (100)(110), [001]-tilt Y-ZrO2 bicrystal

The microstructure of an artificial grain boundary in an YBa 2 Cu 3 O 7-σ (YBCO) thin film grown on a (100)(110), [001]-tilt yttria-stabilized-zirconia (YSZ) bicrystal substrate has been studied using transmission electron microscopy (TEM). The orientation relationship between the YBCO film and the YSZ substrate was [001] YBCO ‖[001] YSZ and [110] YBCO ‖[100] YSZ for each half of the bicrystal film. However, the exact boundary geometry of the bicrystal substrate was not transferred to the film. The substrate boundary was straight while the film boundary was wavy. In several cases there was bending of the lattice confined within a distance of a few basal-plane lattice spacings from the boundary plane and microfaceting. No intergranular secondary phase was observed but about 25% of the boundary was covered by c -axis-tilted YBCO grains and a -axis-oriented grains, both of which were typically adjacent to CuO grains or surrounded by a thin Cu-rich amorphous layer.