Aberration-corrected HRTEM of defects in strained La₂CuO₄ thin films grown on SrTiO₃

The structure of lattice defects in thin La₂CuO₄ films grown under tensile strain on SrTiO₃ (001) is investigated by the combination of state-of-the-art medium voltage aberration-corrected transmission electron microscopy together with numerical exit-plane wavefunction reconstruction. The interfacial reconstruction, the coordination in planar shear defects evolving from surface steps and misfit dislocations of the b = a[010] type are atomically resolved and analysed. Quantitative mapping and evaluation of peak data related to cation atom columns reveal the formation of a perovskite-like layer of lanthanum copper oxide analogous to the thermodynamically instable LaCuO_3−δ phase and a distortion in the octahedral coordination of copper at the interface to the substrate. The planar shear defects embody extra sites for cations and oxygen in a three-dimensional periodic arrangement which are partially filled and provide paths for vacancy hopping transport. The central structure of the misfit dislocation does not exhibit mirror symmetry around a plane containing the dislocation line owing to the asymmetric arrangement of cation columns.