Unraveling Shear Strain Induced Ferroelectric-to-Antiferroelectric Phase Transition and Accessing Intrinsic Antiferroelectricity in Two-dimensional NbOCl2

Abstract: Compared to the well studied two-dimensional (2D) ferroelectricity, much rare is the appearance of 2D antiferroelectricity, where local dipoles from the nonequivalent sublattices within 2D monolayers are oppositely orientated. Using NbOCl2 monolayer with competing ferroelectric (FE) and antiferroelectric (AFE) phases as a 2D material platform, we demonstrate the emerging of intrinsic antiferroelectricity in NbOCl2 monolayer under the experimentally accessible shear strain, and new functionality associated with electric field induced AFE-to-FE phase transition. Specifically, the complex configuration space accommodating FE and AFE phases, polarization switching kinetics and finite temperature thermodynamic properties of 2D NbOCl2, are all accurately predicted by large-scale molecular dynamic (MD) simulations based on deep learning interatomic potential (DP) model. Moreover, room temperature stable antiferroelectricity with low polarization switching barrier and one-dimensional (1D) collinear polarization arrangement is predicted in shear deformed NbOCl2 monolayer. Transition from AFE to FE phase in 2D NbOCl2 can be triggered by the low critical electric field, leading to the double polarization-electric (P-E) loop with small hysteresis. A new type optoelectronic device composed of AFE-NbOCl2, enabling electric "writing" and nonlinear optical "reading" logical operation with fast operation speed and low power consumption is also proposed.