Topographic Study on Ferroelectric NaNO₂ Crystals. I. Structure of 180° Domain Walls

Abstract

180° domain walls have been observed on X-ray diffraction topographs of sodium nitrite (NaNO 2 ) single crystals. Contrast of the walls depends on the kinds of the Bragg reflections used for the topographs. The reflection dependence of the contrast suggests that the contrast is produced neither by strain field around the domain walls nor misorientation of the lattice in the domain walls. A model of the crystal structure of the walls which is consistent with the observed contrast is presented. Thickness of the walls is estimated as the order of 1µm on X-ray topographs and 0.3∼1.0 µm on electron micrographs of replica films extracted from polar surfaces of the crystal.