Domain walls in a perovskite oxide with two primary structural order parameters: First-principles study of BiFeO3

Oswaldo Diéguez,Pablo Aguado-Puente,Javier Junquera,Jorge Íñiguez

doi:10.1103/physrevb.87.024102

Abstract

We present a first-principles study of ferroelectric domain walls (FE-DWs) in multiferroic BiFeO$_3$ (BFO), a material in which the FE order parameter coexists with anti-ferrodistortive (AFD) modes involving rotations of the O$_6$ octahedra. We find that the energetics of the DWs are dominated by the capability of the domains to match their O$_6$ octahedra rotation patterns at the plane of the wall, so that the distortion of the oxygen groups is minimized. Our results thus indicate that, in essence, it is the discontinuity in the AFD order parameter, and not the change in the electric polarization, what decides which crystallographic planes are most likely to host BFO's FE-DWs. Such a result clearly suggests that the O$_6$ rotational patterns play a primary role in the FE phase of this compound, in contrast with the usual (implicit) assumption that they are subordinated to the FE order parameter. Our calculations show that, for the most favorable cases in BFO, the DW energy amounts to a several tens of mJ/m$^2$, which is higher than what was computed for other ferroelectric perovskites with no O$_6$ rotations. Interestingly, we find that the structure of BFO at the most stable DWs resembles the atomic arrangements that are characteristic of low-lying (meta)stable phases of the material. Further, we argue that our results for the DWs of bulk BFO are related with the nanoscale-twinned structures that Prosandeev et al. [Adv. Funct. Mats. (2012), doi: 10.1002/adfm.201201467] have recently predicted to occur in this compound, and suggest that BFO can be viewed as a polytypic material. Our work thus contributes to shape a coherent picture of the structural variants that BFO can present and the way in which they are related.

Highlights

Ferroelectric (FE) crystals are insulators displaying a macroscopic polarization that can be switched by the action of an electric field
The vast majority of the recent discoveries on ferroelectric domain walls (FE-domain wall (DW)) have featured multiferroic BiFeO3, a material that has concentrated many experimental efforts during the past decade because of the promise it holds for room-temperature applications based on magnetoelectric effects
Our finding that the most stable DW configuration is precisely [111](100)[11 ̄1 ̄] 2/1 might seem somewhat arbitrary; on the contrary, this result leads to very suggestive conclusions. In this DW, the AFD component that changes sign is the one perpendicular to the wall; if we focus on the two planes of octahedra next to the DW, we see that they display a a+b−b− Glazer rotation pattern, i.e., the O6 tilts occur in phase (+ superscript) about the [100] direction perpendicular to the DW and in antiphase (− superscript) about the [010] and [001] directions within the DW plane

Summary

Introduction

Ferroelectric (FE) crystals are insulators displaying a macroscopic polarization that can be switched by the action of an electric field. The vast majority of the recent discoveries on FE-DWs have featured multiferroic BiFeO3 (bismuth ferrite or BFO), a material that has concentrated many experimental efforts during the past decade because of the promise it holds for room-temperature applications based on magnetoelectric effects.. The vast majority of the recent discoveries on FE-DWs have featured multiferroic BiFeO3 (bismuth ferrite or BFO), a material that has concentrated many experimental efforts during the past decade because of the promise it holds for room-temperature applications based on magnetoelectric effects.6 For all these reasons, currently there is a strong interest in improving our atomistic understanding of FE-DWs, in particular in the case of BFO The presence of DWs in a material can cause important changes to its macroscopic behavior. for example, recent findings about the conducting and photovoltaic properties of ferroelectric DWs (FE-DWs) have fostered the interest in using them as functional parts in devices in nanoelectronics. The vast majority of the recent discoveries on FE-DWs have featured multiferroic BiFeO3 (bismuth ferrite or BFO), a material that has concentrated many experimental efforts during the past decade because of the promise it holds for room-temperature applications based on magnetoelectric effects. For all these reasons, currently there is a strong interest in improving our atomistic understanding of FE-DWs, in particular in the case of BFO

Methods

Results

Conclusion