Buried In-Plane Ferroelectric Domains in Fe-Doped Single-Crystalline Aurivillius Thin Films

Aurivillius phases constitute a promising class of materials displaying excellent ferroelectric properties, which make them fascinating potential candidates for ferroelectric-based devices. In this perspective, however, the realization of Aurivillius thin films still represents an open challenge. In this work, high-quality single-crystalline Bi 5 FeTi 3 O 15 Aurivillius thin films are grown by pulsed laser deposition. Their structural and polar properties are elucidated by combining several atomic-resolution scanning transmission electron microscopy (STEM) techniques. Our results prove that epitaxial strain is released by the formation of out-of-phase boundaries and the Fe dopant atoms are distributed with a preferential mixed configuration—that is, occupying one inner and one outer site of the four perovskite blocks. The results demonstrate that out-of-phase boundaries are not detrimental for the local ferroelectric polarization, whose value is in agreement with the one predicted by theory. By means of differential-phase contrast (DPC-)STEM and atomic resolution displacement mapping, we demonstrate the presence of buried in-plane ferroelectric domains with the domain walls localized at the Bi 2 O 2 layers. In particular, our results prove that DPC-STEM enables mapping buried polar domains not accessible by surface techniques.