Atomic structure of a Σ=3, {111} twin-boundary junction in a BaTiO₃ thin film

The atomic structure of a multiple-twin-lamella junction in a BaTiO₃film has been investigated by means of high-resolution electron microscopy. The investigation is not based on the direct study of the experimental micrographs but on the study of the quantum-mechanical electron wavefunction emerging from the object. The electron wavefunction is obtained by means of numerical reconstruction procedures which use as input a series of high-resolution micrographs taken from the same object area with different settings of the objective lens defocus. In the observed junction area, four types of twin variant including two groups of nanotwins meet each other, resulting in a complicated boundary structure with a mixture of Σ= 27 and Σ= 3 segments. This junction can be regarded as a grain boundary connecting two BaTiO₃hexagonal structure domains composed of two groups of nanotwins. A boundary structure unit is identified in which some of the BaO[110] columns are found to be partially occupied.