TEM investigation of grain boundaries in Yba_2Cu_3O_7 thin films grown on SrTiO_3 bicrystal substrates

摘要

Thin films of Yba_2Cu_3O_7 were deposited on symmetrical [001]-tilt bicrystals of SrTiO_3 with misorientation angles of 10°, 15°, 24°, 36° and 45°. The grain boundaries in the substrates and the films were investigated by transmission electron microscopy. The substrate grain boundaries were found to be nearly rectilinear and symmetrical, while the film boundaries were dominantly asymmetrical and exhibited a roughness of 20 nm to 200 nm. The roughness of the grain boundaries in films deposited by the pulsed laser ablation is lower than that in sputtered films. The film grain boundaries were 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. The atomic order at the grain boundary was found to be perturbed within one or two interatomic spacings from the interface.