Investigation of the structure of ferroelectric domain boundaries by transmission electron microscopy

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Abstract
A transmission electron microscopy investigation has been conducted on the structure of 90° and 180° domain boundaries in polycrystalline BaTiO3. When such boundaries were imaged with a continuous set of lattice planes, fringes were observed, indicating a stacking‐fault‐type displacement of the crystal lattices on either side of the boundaries. For a 90° domain boundary, this displacement most likely consists of both a dilatation and shear of {110} planes parallel to the boundary plane. The displacement for a 180° boundary lies approximately parallel to [101̄] and is of a greater magnitude. Structural models of both types of boundaries are derived from the observed displacements. The models suggest a distortion of the crystal structure in the boundary region. This distortion allows the polarization vector to simultaneously rotate and decrease in magnitude to zero at the center of the boundary, resulting in the required 90° or 180° rotation of the vector. The presence of the displacement associated with the 180° boundary suggests a substantial boundary thickness, in contradiction to previous models.