Domain boundary structures of flux-grown polydomain lead titanate sing
le crystals have been studied using transmission electron microscopy.
Inclined 90 degrees and 180 degrees domain boundaries show fringe cont
rast and were systematically analyzed under various diffraction condit
ions. Although 90 degrees domain boundaries are supposedly delta-type
boundaries in BaTiO3, our results show that displacement plays an impo
rtant role at boundaries and that the extreme fringe contrast (EFC) be
havior of 90 degrees boundaries is of the (alpha,delta)-mixed type. In
the present work, an analysis based upon the two-beam dynamic theory
was conducted and a selection rule similar to stacking-fault contrast
analysis was established to predict the geometric configuration of 180
degrees domain boundaries using EFC behavior. Examples are given and
verified by tilting experiments and electron diffraction. The results
are highly consistent and offer a convenient way to distinguish betwee
n 90 degrees and 180 degrees boundaries.