Charged Domain Walls and Crystallographic Microstructures in Hybrid Improper Ferroelectric Ca_3−xSr_xTi₂O₇

Abstract

The charged domain walls in ferroelectric materials exhibit intriguing physical properties. We examine herein the charged-domain-wall structures in Ca_3−xSr_xTi₂O₇ using transmission electron microscopy. When viewed along the [001] axis, the wavy charged domain walls are observed over a wide range (>5 µm). In contrast, short charged-domain-wall fragments (from 10 to 200 nm long) occur because they are intercepted and truncated by the conventional 180° domain walls. These results reveal the unusual charged domain structures in Ca_3−xSr_xTi₂O₇ and will be useful for understanding their formation process.

Dark-field images using the reflections (a) 300 and (b) 202 in Ca_3−xSr_xTi₂O₇ (x = 0.45). (a) Charged domain walls (CDWs) and antiphase boundary are visualized. (b) Both head-to-head and tail-to-tail CDWs appear in several regions in addition to the planar 180° domains. The red arrows P indicate the electric polarization directions at each domain. The crystallographic axis [001] is indicated in the images.