Domain-Wall Orientations and Wall Energies in Ferroelectric Triglycine Selenate Crystals

Detailed observations of domain structure in triglycine selenate crystals have been made in special respect to the orientations of the 180° domain-walls by an improved powder-deposition technique. Two kinds of flat wall can be seen; one is parallel to the crystallographic (001) planes and another is to the (201) planes. The angular dependence of the wall-energy density has been numerically calculated on the basis of the Zhirnov-type continuum theory. Two minima in the energy are obtained, each of which corresponds to the wall orientations observed experimentally. The numerical values of elastic stiffness, electrostrictive, dielectric constants and correlation-energy coefficients required for the calculation have been also determined experimentally. The theoretical and experimental results of wall orientations are discussed in comparison with those of triglycine sulfate crystals.