Quasi-one-dimensional ferroelectricity and piezoelectricity in WO$X_4$ halogens

TL;DR

This study explores the ferroelectric and piezoelectric properties of WO$X_4$ halogen compounds with quasi-one-dimensional chains, revealing their potential for high-density ferroelectric memory applications through first-principles calculations.

Contribution

It provides a detailed first-principles analysis of the structure, electronic, ferroelectric, and piezoelectric properties of WO$X_4$ compounds, highlighting their unique quasi-one-dimensional ferroelectricity.

Findings

Polarization magnitudes comparable to perovskites

Low inter-chain domain wall energy density

Potential for hundreds of terabytes per square inch memory density

Abstract

A series of oxytetrahalides WO$X_4$ ($X$: a halogen element) that form quasi-one-dimensional chains is investigated using first-principles calculations. The crystal structures, electronic structures, as well as ferroelectric and piezoelectric properties are discussed in detail. Group theory analysis shows that the ferroelectricity in this family originates from an unstable polar phonon mode $\Gamma_1^-$ induced by the W's $d^0$ orbital configuration. Their polarization magnitudes are found to be comparable to widely used ferroelectric perovskites. Because of its quasi-one-dimensional characteristics, the inter-chain domain wall energy density is low, leading to loosely-coupled ferroelectric chains. This is potentially beneficial for high density ferroelectric memories: we estimate that the upper-limit of memory density in these compounds could reach hundreds of terabytes per square inch.