Phase instability induced by polar nanoregions in a relaxor ferroelectric system

TL;DR

This study reveals how polar nanoregions influence the structural dynamics of relaxor ferroelectrics, affecting sound wave propagation and potentially contributing to their exceptional piezoelectric properties.

Contribution

It demonstrates the significant impact of polar nanoregions on phonon behavior and phase stability in relaxor ferroelectrics using neutron inelastic scattering.

Findings

PNR strongly interacts with acoustic phonons.

Asymmetry in lattice dynamics caused by PNR.

PNR-phonon interaction may lead to phase instability.

Abstract

Local inhomogeneities known as polar nanoregions (PNR) play a key role in governing the dielectric properties of relaxor ferroelectrics - a special class of material that exhibits an enormous electromechanical response and is easily polarized with an external field. Using neutron inelastic scattering methods, we show that the PNR can also significantly affect the structural properties of the relaxor ferroelectric Pb(Zn1/3Nb2/3)O3-4.5%PbTiO3 (PZN-4.5%PT). A strong interaction is found between the PNR and the propagation of sound waves, i.e. acoustic phonons, the visibility of which can be enhanced with an external electric field. A comparison between acoustic phonons propagating along different directions reveals a large asymmetry in the lattice dynamics that is induced by the PNR. We suggest that a phase instability induced by this PNR-phonon interaction may contribute to the ultrahigh piezoelectric response of this and related relaxor ferroelectric materials. Our results also naturally explain the emergence of the various observed monoclinic phases in these systems.