# Stable Charged Antiparallel Domain Walls in Hyperferroelectrics

## TL;DR

This paper investigates the stability and electronic properties of charged antiparallel domain walls in hyperferroelectrics and canonical ferroelectrics, revealing their potential to support conductive electron gases.

## Contribution

It demonstrates the stabilization of charged 180° domain walls in hyperferroelectrics and ferroelectrics without dopants, and explores their electronic effects using density functional theory.

## Key findings

- Charged domain walls can be stabilized in hyperferroelectrics and LiNbO₃.
- Charged walls can reduce or close the band gap.
- Charged walls support quasi-two-dimensional electron/hole gases.

## Abstract

Charge-neutral 180$^\circ$ domain walls that separate domains of antiparallel polarization directions are common structural topological defects in ferroelectrics. In normal ferroelectrics, charged 180$^\circ$ domain walls running perpendicular to the polarization directions are highly energetically unfavorable because of the depolarization field and are difficult to stabilize. We explore both neutral and charged 180$^\circ$ domain walls in hyperferroelectrics, a class of proper ferroelectrics with persistent polarization in the presence of a depolarization field, using density functional theory. We obtain zero temperature equilibrium structures of head-to-head and tail-to-tail walls in recently discovered $ABC$-type hexagonal hyperferroelectrics. Charged domain walls can also be stabilized in canonical ferroelectrics represented by LiNbO$_3$ without any dopants, defects or mechanical clamping. First-principles electronic structure calculations show that charged domain walls can reduce and even close the band gap of host materials and support quasi-two-dimensional electron(hole) gas with enhanced electrical conductivity.