Theoretical study on two dimensional group IV-VI ternary compounds with large in-plane spontaneous polarization

Abstract

Room temperature ultra-thin ferroelectric materials are highly desired for a wide range of applications, such as high-density non-volatile memory devices. However, the continuous thinning of the ferroelectric film is impeded by the enhanced depolarization field. Recently demonstrated two-dimensional (2D) ferroelectric sheds the light on the realization of atomically thin ferroelectric materials for advanced applications. Herein, through comprehensive first-principles calculations, we successfully designed several Janus type 2D group IV-VI ternary compounds M2XY (M = Ge, Sn; X/Y = S, Se) and ABN2 (A/B = Ge, Sn; N = S, Se) with large in-plane ferroelectric polarization. Specifically, we show that via Janus substitution to break the original symmetry, the in-plane ferroelectric polarization of the 2D ternary compounds can be tuned from 3.82 to 5.03*10−10C/m. The effective modulation of the spontaneous polarization of 2D group IV-VI ternary compounds in response to the external strain is also revealed. The bandgaps of these 2D ternary compounds are in the range of 1.6 to 2.0 eV. The dynamics and thermal stabilities of these ternary compounds were also confirmed by the phonon spectrum calculations and ab initio molecular dynamics (AIMD) simulations. The AIMD simulation also indicate that the ferroelectric order of these ternary compounds can be maintained at room temperature. This study not only expand the size of the 2D ferroelectrics family but also demonstrates a feasible strategy to tune the polarization of 2D ferroelectric materials.