Auxetic B₄N Monolayer: A Promising 2D Material with in-Plane Negative Poisson's Ratio and Large Anisotropic Mechanics

Auxetic materials, known with negative Poisson's ratio, are highly desirable for many advanced applications, but the candidates are rather scarce, especially at low dimension. Motivated by the re-entrant structure that often exposes negative Poisson's ratio, we predict a two-dimensional (2D) planar B₄N monolayer as a promising auxetic material with unusual in-plane negative Poisson's ratio within the framework of density functional theory calculations. B₄N monolayer also exhibits a highly emerged mechanical anisotropy, characterized by Young's modulus and Poisson's ratio. In addition, this monolayer shows superior mechanical flexibility in ideal tensile strength and critical strain values. The phonon dispersion calculations and ab initio molecular dynamics simulations further demonstrate that this monolayer also owns excellent dynamical and thermal stabilities. The fantastic mechanical properties coupled with robust structural stability render the auxetic B₄N monolayer promising for future nanomechanical devices.