Figure 3. ABF-STEM imaging of oxygen vacancy ordering in La_1−xSr_xCoO_3−δ (x=0.8, 1.0).

(a) [001]_p ABF-STEM image of LSCO28 showing the cation and anion sublattices. The contrast is inverted in comparison with the HAADF-STEM images. The assignment of the atomic columns is shown in the enlargement at the top right corner. Half of the perovskite (CoO₂) layers appear brighter indicating oxygen deficiency (marked with white arrowheads). The complete (CoO₂) layers and anion-deficient (CoO_2−δ) layer alternate (see the ABF intensity profile below, the anion-deficient layers are marked with black arrowheads) resulting in doubling of the perovskite lattice parameter in the direction perpendicular to the layers. (b) [001]_P ABF-STEM image of SCO showing layered anion-vacancy ordering. The (CoO_2−δ) layers are marked with the white arrowheads and demonstrate the contrast clearly distinct from that of the (CoO₂) layers. The assignment of the atomic columns is shown in the enlarged part at the bottom left.