First-principles study of ferroelectricity in two-dimensional quin-layer M₂CT₂ MXenes

In this work, the ferroelectricity of a group of quin-layer M 2 CT 2 monolayer MXenes compounds is investigated from first principles. The polar H phase of Sc 2 CS 2 , Sc 2 CSe 2 , Y 2 CS 2 , and Y 2 CSe 2 are predicted by our results which show the co-existence of out-of-plane (OOP) and in-plane (IP) electric polarizations. We clarified that the spontaneous OOP polarization in the H phase originated from the high-order coupling with IP polarization. The competition between the FE and anti-ferroelectric state of studied H phase monolayer M 2 CT 2 MXenes is investigated as well. Compared with previously reported Mixed-phase for M 2 CT 2 MXenes, the H phase presents strong coupling between OOP polarizations and external electric field making them more feasible for manipulating in practical applications.