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.
@article{arxiv.2406.00293,
title = {Ferroelectricity in oxygen-terminated 2D carbides of lanthanide elements},
author = {Lin Han and Wencong Sun and Pingwei Liu and Xianqing Lin and Dan Liu and David Tomanek},
journal= {arXiv preprint arXiv:2406.00293},
year = {2024}
}