The structure of [001] tilt boundaries in thin films deposited onto [001] tilt SrTiO3 bicrystal substrates was characterized by transmission electron microscopy. These boundaries were (100)/(210), (310)/(510), (410)/(310), (510)/(210), (210)/(410), and (210)/(310), with corresponding misorientation angles of 26°, 29°, 32°, 37°, 40° and 44°. It was found that the Cu3Ba2YO7 film boundaries meandered along the relatively straight substrate boundaries. High-resolution lattice images indicated that the microscopic meandering of the film boundary essentially consisted of many straight segments of facets at the atomic scale. On the basis of the observed facets, three competing factors controlling the formation of facets were identified. First, the boundary plane was defined by Miller indices (hk0) in both crystals with sufficiently small h, k (i.e., h, k ≤ 5) and sufficiently large effective interplanar spacing (i.e., deff > 0.06nm). Second, the closure failure defined by the difference between the local misorientation from the design misorientation was small, i.e., less than 2°. Third, the deviation of a local facet plane was observed to be less than 30° from the design boundary plane.

Grain Boundary Faceting in YBa2Cu3O7-x Bicrystal Thin Films on SrTiO3 Substrates. Q.Jin, S.W.Chan: Journal of Materials Research, 2002, 17[2], 323-35