Anomalous pressure dependence of the atomic displacements in the relaxor ferroelectric PbMg$_{1/3}$Ta$_{2/3}$O$_3$

TL;DR

This study investigates how hydrostatic pressure affects atomic displacements in the relaxor ferroelectric PbMg$_{1/3}$Ta$_{2/3}$O$_3$, revealing a significant decrease in lead displacement and increased oxygen anisotropy, which relate to dielectric and scattering properties.

Contribution

It provides new insights into pressure-induced atomic displacement changes in relaxor ferroelectrics using neutron diffraction, highlighting the role of lead and oxygen atoms.

Findings

Lead displacement decreases drastically under pressure.

Oxygen atom anisotropy increases by about 50%.

Magnesium/Tantalum vibrations are pressure insensitive.

Abstract

The crystal structure of the PbMg$_{1/3}$Ta$_{2/3}$O$_3$ (PMT) relaxor ferroelectric was studied under hydrostatic pressure up to $\sim 7$ GPa by means of powder neutron diffraction. We find a drastic pressure-induced decrease of the lead displacement from the inversion centre which correlates with an increase by $\sim$ 50 % of the anisotropy of the oxygen temperature factor. The vibrations of the Mg/Ta are, in contrast, rather pressure insensitive. We attribute these changes being responsible for the previously reported pressure-induced suppression of the anomalous dielectric permittivity and diffuse scattering in relaxor ferroelectrics.