Domain-wall pinning and defect ordering in BiFeO3 probed on the atomic and nanoscale

Andreja Bencan,Tadej Rojac,Hana Ursic,Goran Drazic,Maja Makarovic,Matej Komelj

doi:10.1038/s41467-020-15595-0

Andreja Bencan, Tadej Rojac + Show 4 more

Open Access

https://doi.org/10.1038/s41467-020-15595-0

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Abstract

Electro-mechanical interactions between charged point defects and domain walls play a key role in the functional properties of bulk and thin-film ferroelectrics. While for perovskites the macroscopic implications of the ordering degree of defects on domain-wall pinning have been reported, atomistic details of these mechanisms remain unclear. Here, based on atomic and nanoscale analyses, we propose a pinning mechanism associated with conductive domain walls in BiFeO3, whose origin lies in the dynamic coupling of the p-type defects gathered in the domain-wall regions with domain-wall displacements under applied electric field. Moreover, we confirm that the degree of defect ordering at the walls, which affect the domain-wall conductivity, can be tuned by the cooling rate used during the annealing, allowing us to determine how this ordering affects the atomic structure of the walls. The results are useful in the design of the domain-wall architecture and dynamics for emerging nanoelectronic and bulk applications.

Highlights

Electro-mechanical interactions between charged point defects and domain walls play a key role in the functional properties of bulk and thin-film ferroelectrics
While impressive progress has been made in the nanotechnology, engineering and macroscopic implications of conductive domain walls (DWs), little has been done to understand the atomistic details of their dynamics under applied electric fields
Since the discovery of conductive DWs in multiferroic BiFeO3 thin films, it has been suggested that the local conductivity should be enhanced by the presence of charged point defects accumulated inside DW regions[3]

Summary

Introduction

Electro-mechanical interactions between charged point defects and domain walls play a key role in the functional properties of bulk and thin-film ferroelectrics. The reason is that such interfaces can be displaced, written and erased by external electrical[3] or stress fields[4] Coupled with their electrical conductivity, which can be engineered[5,6,7], spatially tunable DWs could provide a controllable way to design conductive paths on the nanoscale[8], resulting in DW diodes[9], memories[10,11] and switches[12]. In the case of air-processed polycrystalline BiFeO3, the accumulated defects at the head-to-tail DWs were directly identified by atomic-resolution microscopy as Bi vacancies and electron holes[21] The latter were revealed to be localized at Fe3+ sites, creating Fe4+ oxidized states, and were experimentally confirmed to be responsible for the p-type DW conduction in polycrystalline BiFeO3. In addition to the type of defects, the DW pinning strongly depends on the spatial distribution of defects, often conceptualized in terms of the “order/disorder” defect state[16,28,29]

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