Atomically resolved structure of step-like uncharged and charged domain walls in polycrystalline BiFeO3

Naonori Sakamoto,Tadej Rojac,Oana Condurache,Andreja Benčan,Goran Dražić

doi:10.1063/5.0034699

Abstract

The dynamics of domain walls (DWs) during polarization switching has a great influence on the electromechanical response of ferroelectrics. To understand the influence of DWs on the functional performance of the material, their local structure and properties must be revealed. There are many investigations of the DWs in ferroelectric thin films, while investigations of the DWs in polycrystalline ferroelectrics are fewer. Here, we report on a comparative study of uncharged and charged (“tail-to-tail”) DWs in BiFeO3 ceramics from the point of view of the atomically resolved strain and structure using scanning-transmission electron microscopy. Both types of DWs have a step-like morphology and have a non-Ising behavior. The strain, expressed as the unit-cell distortion, is higher and more concentrated in the case of uncharged walls, which we associate with a narrower transition region of the Fe-displacement vectors. Conversely, in the case of “tail-to-tail” charged DWs, the unit-cell distortion is smaller and more dispersed because of the wider transition region of the Fe-displacement vectors. All the types of step-like DWs reported here, regardless of their charge state, exhibit a comparable amount of Bi-vacancies segregation. Further details about the structural differences are discussed from the point of view of the Fe-displacement evolution through the wall for uncharged/“tail-to-tail” charged DWs. The results are useful as they provide an insight into the local structure and chemistry of charged and uncharged DWs in polycrystalline BiFeO3.

Highlights

Domain walls (DWs) in ferroelectrics are nanoscale topological features that mark the transition between regions with homogeneous orientations of the polarization
We present three kinds of {100}pc-type domain walls (DWs): (1) an uncharged DWs (UDWs) having step-like features [DW1 in Fig. 1(d)]; (2) a charged DWs (CDWs) that has similar steps to DW1 [DW2 in Fig. 1(e)] and (3) a wall that has a quasi-rectangular step, having charged/uncharged segments [DW3 in Fig. 1(f )]
We have shown that the morphology of both types of {100}pc-type DWs can be complex and form step-like kinks

Summary

Introduction

Domain walls (DWs) in ferroelectrics are nanoscale topological features that mark the transition between regions with homogeneous orientations of the polarization. The unique electrical properties that the walls can possess, in combination with their dynamic nature under an applied electric field, provide to the DWs with the potential to become “the device.”[3] New applications have been proposed for so-called “non-volatile, ferroelectric, domain-wall memories,” where the memory binary state, rather than relying on the conventional polarization state during domain switching, is determined by writing and erasing a particular conductive DW in BiFeO3 (BFO).[4] Second, the interphases in ferroelectrics together with the intrinsic lattice distortion can significantly affect the macroscopic electromechanical response of the material.[5,6,7,8] For example, in (K,Na)NbO3-based ceramics, it has been shown that up to 80% of the electric-field-induced macroscopic strain, which is important in, e.g., piezoelectric actuators, can originate from a non-180° DW-switching contribution.[9]

Methods

Results

Conclusion