Ferroelectricity in oxygen-terminated 2D carbides of lanthanide elements

TL;DR

This study explores oxygen-terminated 2D lanthanide carbides, revealing their ferroelectric and anti-ferroelectric phases, strain-induced phase transitions, and promising optical properties for ultraviolet photon absorption.

Contribution

It introduces a new class of 2D lanthanide carbides with ferroelectric properties and strain-tunable electronic phases, expanding potential applications in optoelectronics.

Findings

Oxygen termination induces semiconducting behavior in M2C monolayers.

Alpha-phase is ferroelectric, beta-phase is anti-ferroelectric.

Strain can switch phases and tune electronic properties.

Abstract

We investigate the properties of oxygen-functionalized carbides of lanthanide elements with the composition M2CO2 (M=Gd, Tb,Dy) that form two-dimensional (2D) structures. Our ab initio calculations reveal that oxygen termination turns M2C monolayers into semiconductors with two dynamically stable phases. Of these, the energetically favored alpha-phase becomes ferroelectric, whereas the beta-phase turns anti-ferroelectric. Applying in-plane biaxial strain may transform one phase into the other, changes the ferroelectric polarization of the alpha-phase in a linear fashion, and modifies the size and nature of the fundamental band gap from direct to indirect. The structure with a direct band gap exhibits in-plane isotropic electronic and optical properties. This previously unexplored class of systems also exhibits excellent photon absorption in the ultraviolet range.