Frequency-dependent decoupling of domain-wall motion and lattice strain in bismuth ferrite

Lisha Liu,John Daniels,Tadej Rojac,Marco Di Michiel,Dragan Damjanovic

doi:10.1038/s41467-018-07363-y

Abstract

Dynamics of domain walls are among the main features that control strain mechanisms in ferroic materials. Here, we demonstrate that the domain-wall-controlled piezoelectric behaviour in multiferroic BiFeO3 is distinct from that reported in classical ferroelectrics. In situ X-ray diffraction was used to separate the electric-field-induced lattice strain and strain due to displacements of non-180° domain walls in polycrystalline BiFeO3 over a wide frequency range. These piezoelectric strain mechanisms have opposing trends as a function of frequency. The lattice strain increases with increasing frequency, showing negative piezoelectric phase angle (i.e., strain leads the electric field), an unusual feature so far demonstrated only in the total macroscopic piezoelectric response. Domain-wall motion exhibits the opposite behaviour, it decreases in magnitude with increasing frequency, showing more common positive piezoelectric phase angle (i.e., strain lags behind the electric field). Charge redistribution at conducting domain walls, oriented differently in different grain families, is demonstrated to be the cause.

Highlights

Dynamics of domain walls are among the main features that control strain mechanisms in ferroic materials
The ferroelectric material BiFeO3 has been demonstrated to possess enhanced electrical conductivity at domain walls[2]. This material displays Maxwell–Wagnerlike frequency dispersion in its macroscopic piezoelectric response[7]. This dispersion is different from a prototypical frequency dependent behaviour of the piezoelectric coefficient in classical ferroelectric materials, such as soft Pb(ZrxTi1−x)O3 (PZT)
The converse piezoelectric response to an applied electric field has its origin in several structural features, for example, small displacements of atoms under external fields in the crystal unit cell, i.e., the lattice strain, motion of non-180° domain walls resulting in a change in ferroelectric/ferroelastic domain texture, and electric-fieldinduced phase transformations

Summary

Introduction

Dynamics of domain walls are among the main features that control strain mechanisms in ferroic materials. We demonstrate by using time-resolved in situ XRD and analytical modelling that the distinct frequency dependent piezoelectric behaviour in polycrystalline BiFeO3 is due to conducting domain walls.

Results

Conclusion