First-principles Study Of Ferroelectricity In Two-dimensional Materials

In recent years,Ferroelectric materials have been one of the intensively studied field in condensed matter physics and materials science.Ferroelectric materials have been from the original piezoelectric ceramic materials to the perovskite ferroelectric materials,and they’re ferroelectric thin film materials at present.Ferroelectric materials are improved in the direction of smaller and easier to integrate devices,and they have a wide range of applications.It is necessary to find ferroelectric materials which have spontaneous polarization and whose polarization can be artificially modulated and reversed.That has great significance for the development of new information storage materials.Due to the net charge on the surface,depolarization field is generated inside the traditional 3D ferroelectric material.That inhibits the spontaneous polarization of the 3D ferroelectric material whose film is less than a certain thickness,it seriously restricts the device miniaturization and the application of high integration direction.Therefore,it is very important to find and study two-dimensional ferroelectric materials with stable spontaneous polarization.In our study,we will focus on two-dimensional single-layer ferroelectric materials through the DFT calculation.Based on the system symmetry analysis,we explored two-dimensional materials with spontaneous polarization,especially the ones with out-of-plane polarization.In our study,we notice that in-plane strain is able to tune the ferroelectric behaviors of twodimensional materials,induce the transition between ferroelectric phase and paraelectric phase.We investigated some related behavior such as the inversion of polarization and the coupling between lattice modes via our first-principles calculations.Based on which,the phenomenological Landau model was built as well in order to better show the coupling between in-plane and out-of-plane polarization.Our research reveals some fundamental rules of two-dimensional ferroelectric behavior,and provides new pathway of exploring novel two-dimensional ferroelectric and multi-ferro materials.