First principles studies of the Born effective charges and electronic dielectric tensors for the relaxor PMN (PbMg1/3Nb2/3O3)

TL;DR

This study uses first principles calculations to analyze the Born effective charges and dielectric properties of the relaxor material PMN, revealing microscopic insights and identifying a monoclinic ground state with specific chemical ordering.

Contribution

It provides new first principles insights into the microscopic factors influencing piezoelectricity and identifies the ground state structure of PMN with specific chemical ordering.

Findings

Charge ellipsoids reveal polarization rotation effects.

Multiple low-symmetry ferroelectric phases identified.

Ground state is monoclinic C2 with 1:2 chemical order.

Abstract

We report first principles density functional calculations of the Born effective charges and electronic dielectric tensors for the relaxor PMN (PbMg1/3Nb2/3O3). Visualization of the Born charge tensors as charge ellipsoids have provided microscopic insights on the factors governing piezoelectric enhancements with polarization rotation. Several 15 and 30-atom ferroelectric and antiferroelectric supercells of PMN involving 1:2 and 1:1 chemical ordering have been studied. A cascading set of ferroelectric phonon instabilities lead to several low symmetry monoclinic structures. We find a ground state with a 15-atom unit cell with 1:2 chemical ordering along [111] with a monoclinic C2 structure.