Elastic coupling between 90° twin walls and interfacial dislocations in epitaxial ferroelectric perovskites: A quantitative high-resolution transmission electron microscopy study

Abstract

A quantitative high-resolution transmission electron microscopy study has been performed on tetragonal, single-crystalline $\mathrm{Pb}({\mathrm{Zr}}_{0.4}{\mathrm{Ti}}_{0.6}){\mathrm{O}}_{3}$ islands grown on Nb-doped $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}(001)$ substrates, revealing the strain fields of a 90\ifmmode^\circ\else\textdegree\fi{} ferroelastic twin wall and the nearby interfacial dislocation. The twin wall, showing a width of $\ensuremath{\sim}1.5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and compressive strain features, is elastically coupled to the tensile-type strain of an edge dislocation having an out-of-plane Burgers vector, indicating an intimate interaction of the strain fields of both crystallographic defects. The long-range strain field of the dislocation core imposes a potential barrier on the twin wall, limiting its translational mobility under an applied electric field. The substrate clamping in the epitaxial island further acts as a restoring force on the electric-field-induced wall movement. The ensemble of these electromechanical boundary conditions thus indicates that the ferroelastic twin wall in the island should be immobile upon external electric fields. A further discussion also suggests that this complex interplay of the substrate clamping and the interfacial dislocation should account for the reported low twin-wall mobility in continuous, epitaxial ferroelectric perovskite films under an electric field.