Domain structures and planar defects in SrBi₂Ta₂O₉ single crystals observed by transmission electron microscopy

Abstract

In this work, the domain structures and structural planar defects in SrBi2Ta2O9 (SBT) single crystals with (001) orientation were investigated by transmission electron microscopy. The 90° domain walls are identified by the 90° rotation relationship of the electron diffraction pattern about the [001] zone axis, and which exhibit irregular configurations. Antiphase boundaries (APBs) in SBT single crystals are also observed, which exhibit ribbon-like morphologies. Fourfold vertices formed by four APBs meeting together are observed as predominant singularities, and are explained by a four-state clock model, in which the four states are considered as the TaO6 octahedra tilting left, right, forward, or backward along the crystallographic directions. Some threefold vertices are also observed since both threefold and fourfold vertices are energetically allowed in the present model.