A new model of correlated disorder in relaxor ferroelectrics

TL;DR

This paper introduces a phenomenological model for relaxor ferroelectrics like PMN-PT, explaining their dielectric properties and scattering behavior through a specific lead ion displacement pattern influenced by acoustic phonons.

Contribution

It presents a new model linking lead ion displacement dynamics to relaxor behavior, challenging the traditional concept of static polar nanoregions.

Findings

Qualitatively explains temperature, pressure, and electric field effects on scattering.

Accounts for hierarchy in relaxation times.

Disputes the static polar nanoregions concept.

Abstract

We propose a simple phenomenological picture to explain the unusual dielectric properties of the proto-typical ferroelectric relaxor lead magnesium niobate-titanate (PMN-PT). Our model assumes a specific, slowly changing, displacement pattern of the lead ion, which is indirectly controlled by the low-energy acoustic phonons of the system. The model qualitatively explains in great detail the temperature, pressure, and electric field dependence of diffuse neutron- and x-ray scattering, as well as the existence of hierachy in the relaxation times of these materials. We furthermore show that the widely used concept of polar nanoregions as indiviudal static entities is incompatible with the available body of experimental diffuse scattering results.