Figure 4. Unknown AFE-like atomic columns in Sr₇Ti₆O₁₉ film region #2.

(a) Cation u_C and oxygen u_O interatomic spacing (purple open circles) extracted from constructed drift-corrected HAADF and BF STEM images superimposed on the DFT calculated values (black lines). The characteristic decrease in interplanar spacing in u_C and absence in u_O adjacent to the rock salt layers indicates the presence of rumpling at the rock salt layer; exceptional agreement between experiments and DFT is seen. (b) Constructed average HAADF and BF STEM slices, which are repeated for clarity. (c) Cation Δx_C (blue and green open circles) and oxygen Δx_O (red open circles) displacements along the [100]_PC direction measured from the drift-corrected HAADF and BF images. The AFE DFT calculated value (solid black lines) and the AFE STEM simulated Δx_O values (dashed light blue line) are superimposed to show agreement between simulation and experiments. Included in column 2 is the π phase shifted cation positions (dotted black line) for comparison with the STEM data. The simulated Δx_O values (dashed black lines) were done with a 1.25 mrad sample tilt around the [001]_PC axis. The error bars are taken to be the root mean s.e. from the positions of a best fit lattice determined by CV.