Polar phase transition in $180^{\circ}$-domain wall of lead titanate

TL;DR

This paper proposes a new mechanism for switchable polarization in ferroelectric domain walls, explaining the origin of polar components in PbTiO$_3$ through a phase transition triggered by biquadratic coupling.

Contribution

It introduces a novel biquadratic coupling mechanism that causes a phase transition in ferroelectric domain walls, elucidating the emergence of polar components in PbTiO$_3$.

Findings

Identification of a biquadratic coupling mechanism triggering phase transition.

Explanation of polar Bloch and antipolar Néel components in 180°-domain walls.

Prediction of susceptibility increase at the phase transition temperature.

Abstract

A new mechanism leading to a switchable polarization in a ferroelectric domain wall (DW) is proposed. A biquadratic coupling of the primary order parameter and its gradient triggers the phase transition in the DW with softening of the local polar mode and anomalous increase of the susceptibility at the phase transition temperature $T_{DW}$. This mechanism describes the origin and properties of the polar Bloch and antipolar N\'eel components in the $180^\circ$-DW of PbTiO$_3$, which were recently reported from first-principles calculations.