TEM INVESTIGATION OF GRAIN-BOUNDARIES IN YBA2CU3O7 THIN-FILMS GROWN ON SRTIO3 BICRYSTAL SUBSTRATES

Thin films of YBa2Cu3O7 were deposited by high-oxygen-pressure de-sputtering on [001]-tilt bicrystals of SrTiO3 with rotation angles of 10 degrees, 24 degrees, 36 degrees and 45 degrees. The substrates and the films were investigated by transmission electron microscopy. The lateral roughness of the substrate grain boundaries was found to be about 3 nm, white the film grain boundaries exhibited a roughness of 20 nm to 200 nm. The film boundaries were dominantly asymmetrical and faceted so that the grain boundary plane corresponds to a low-index plane of one of the two adjacent grains. The majority of these low-index planes were (100) or (110) planes. Symmetrical segments were only observed for the 24 degrees grain boundary. For the 45 degrees boundary only (100)/(110) facets were found. The atomic structure of a (100)/(110) facet was investigated in detail by comparing the experimental high-resolution electron micrographs with calculated images. The atomic order at the grain boundary was found to be perturbed within one or two interatomic spacings from the interface.