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

The atomic structure of a multiple-twin-lamella junction in a BaTiO3 film h as been investigated by means of high-resolution electron microscopy. The i nvestigation is not based on the direct study of the experimental micrograp hs but on the study of the quantum-mechanical electron wavefunction emergin g from the object. The electron wavefunction is obtained by means of numeri cal reconstruction procedures which use as input a series of high-resolutio n micrographs taken from the same object area with different settings of th e 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 Sigma = 27 and Sigma = 3 s egments. This junction can be regarded as a grain boundary connecting two B aTiO3 hexagonal structure domains composed of two groups of nanotwins. A bo undary structure unit is identified in which some of the BaO[110] columns a re found to be partially occupied.