Ferroelectric domains in pressureless-sintered barium titanate

Ferroelectric domains in pressureless-sintered BaTiO3 ceramics have been studied using scanning and transmission electron microscopy. Both the 90 degrees- and 180 degrees-type exhibiting the characteristic features of herringbones, square-nets, and "water-mark", respectively, are observed in polished sections. Most of the domains identified in thin foils are the conventional 90 degrees a-a type. Unconventional 90 degrees a-a domain boundaries lying on {111} are also identified from the CO2-laser-sintered samples, but they have vanished after several minutes of electron beam irradiation. Both the wedge-shape and overlapped "microtwin" domains exhibit the characteristic delta-fringes. The displacement vector R of [101] is thought to have derived from a small lattice translation introduced by the rotation of the polarization vector across the domain boundaries. Lattice-fringe images of the 90 degrees domain boundaries suggest that the lattice distortion has occurred to accommodate the strain generated by the c --> t-BaTiO3 phase transition. The strain thus induced is manifested by dot contrast appearing on the 90 degrees domain walls as revealed by transmission electron microscopy. The distribution of dots suggests that the strains are taken up inhomogeneously both along and across the domain boundaries by the crystal lattices. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd rights reserved.