Determination of displacement vector on 180 degrees domain boundary and polarization arrangements in lead titanate crystals

180 degrees domain boundaries in flux-grown lead titanate single crystals show intriguing domain boundary extreme fringe contrast using transmission electron microscopy. Symmetrically distributed domain boundaries with alternate contrast have been observed, indicating that opposite displacement vectors exist one by one at boundaries, If appropriate reflection vectors were employed, an inclined domain boundary shows reversed fringe contrast. An analysis based upon the two-beam dynamical theory and a rule similar to stacking-fault contrast analysis was employed to predict the geometric configuration of a 180 degrees domain boundary using the extreme fringe contrast (EFC) behavior. Appropriately choosing reflection Vectors and utilizing the EFC reversal, a displacement vector as well as the polarization vector arrangement across a 180 degrees domain boundary can be unambiguously identified, Employing the information derived from diffraction patterns and a tilting experiment across a nearby 90 degrees boundary, the whole polarization configuration can be uniquely determined.