New phases of 2D group-VA nanostructures with unusual auxetic mechanical properties induced by the regularity of the interatomic interaction force

Abstract

Designing new auxetic materials is important for flexible electronics. The micromechanism of auxeticity in two-dimensional (2D) materials has attracted significant attention but the main factors of auxeticity are case-dependent and their connection with the geometrical/electronic features of 2D materials still requires systematic exploration. In this work, two new phases of 2D group-VA materials, namely, X10-2_2 and X12-14 (X = P, As, Sb, and Bi), were predicted. All these structures were proven to be stable from the aspects of their thermodynamic and kinetic stabilities. Investigations of their electronic properties revealed that these structures were all semiconductors with high anisotropic mobility. Mechanical analyses showed that all the X12-14 phases exhibited auxeticity, whereas the Poisson's ratios of the X10-2_2 series presented a strong dependence on the group-VA elements. The P10-2_2 structure exhibited auxeticity under both tensile and compression strain. However, As10-2_2 exhibited a peculiar half-auxeticity and Sb10-2_2 and Bi10-2_2 were non-auxetic. Evaluations of the interatomic interaction forces revealed that it is the unique folded structures and the changes of the atomic interactions that induce the different mechanical properties of the X10-2_2 structures. This work uncovers the special relationship between the auxeticity of 2D group-VA materials and the inherent natures of the group-VA elements from the viewpoint of the interatomic interaction force, which will assist future research on auxetic materials.