Investigation of atomic displacements at a Σ3 (111) twin boundary in batio₃ by means of phase-retrieval electron microscopy

We applied the technique of focal-series reconstruction in high-resolution electron microscopy for a precise determination of the spacings between atomic columns at a Σ3 (111) twin boundary in perovskite BaTiO₃. We succeeded in observing a predicted expansion of the nearest Ti-Ti spacing across the boundary plane and found additionally a contraction of the nearest BaO-BaO spacing. Moreover, the direct visualization of oxygen columns in the boundary plane is demonstrated. The boundary structure agrees in detail with a subunit of the hexagonal phase of BaTiO₃.