Microstructure of YBa2Cu3O/sub 7-//sub x/ thin films grown on single-crystal SrTiO3

YBa2Cu3O/sub 7-//sub x/ thin films on (001) and (014) SrTiO3 were prepared by coevaporation of Y, BaF2, and Cu, and annealing in oxygen at 850 0C. Cross-sectional samples prepared by cutting films and substrates along the SrTiO3 (100) plane were studied with transmission electron microscopy. The growth of YBa2Cu3O/sub 7-//sub x/ in as-deposited films is extremely anisotropic with the [001] being the slow direction and the (001) plane being the fast growth plane. When the (001) planes of YBa2Cu3O/sub 7-//sub x/ grains are parallel to the film plane, as on (001) SrTiO3, there is a dominance of this orientation over the whole film. Three types of YBa2Cu3O/sub 7-//sub x/ grains, 900 misoriented from each other, are observed to grow on both (001) and (014) surfaces of single-crystal SrTiO3 substrates with their c directions aligned with one of the three <100> directions of cubic SrTiO3. This ambiguity creates a threefold degenerate epitaxy of YBa2Cu3O/sub 7-//sub x/ on SrTiO3, which results in 900 grain boundaries in the final YBa2Cu3O/sub 7-//sub x/ thin films. These boundaries are free of any second phase and decorations. While some extraneous phases were observed in these films, they were located away from the crystallographically special, 900 boundaries. Therefore, the presence of extraneous phases elsewhere in the films was not damaging to the superconducting transport