Theoretical discovery of novel two-dimensional V-A-N binary compounds with auxiticity

Auxetic materials, which possess a negative Poisson's ratio (NPR), have been a hot topic in materials science research. Through atomistic simulations, we theoretically rediscover a few novel two-dimensional (2D) V-A-nitride (V-A-N) binary compounds with delta-phosphorene-like structures. The structures in the delta-phase (except for delta-PN) exhibit better stability in terms of energy, thermodynamics, and mechanics with respect to their counterparts in the alpha- and beta-phases. The structures in the delta-phase show semiconducting behaviors with direct band gaps falling in the visible light region. Interestingly, most structures in the alpha- and delta-phases (except for delta-BiN) exhibit large in-plane NPRs and excellent mechanical properties. The maximum NPR occurs along the zigzag (x) direction for the delta-phases and along the diagonal direction for the alpha-phases. Particularly, for alpha- and delta-SbN, the NPRs are -0.628 and -0.296, respectively. delta-SbN can sustain tensile strains of up to 22% and 35% with maximum stresses of 12.1 and 9.8 GPa in the zigzag and armchair directions, respectively. In addition, the transverse response can reach up to 6.6% at a strain of similar to 18% along the armchair (y) direction for delta-SbN, which is considerably higher than those of other 2D auxetic materials. Our results reveal that 2D V-A-N binary compounds have potential applications in designing 2D electromechanical and optoelectronic devices.