For ordinary materials, the lattices along one direction are extended or contracted as compressed or stretched in other orthogonal directions. Poisson (ν) is a parameter for quantifying physical properties, in most cases. But for some special materials (so-called "expansion materials"), ν can be negative. Negative Po Snesum ratio (NPR) causes great interest because NPR types typically have stronger toughness, shear, and effective noise reduction, so that many novel applications, such as aerospace and National defense, etc. Historically, most of the research on NPR is conducted in the body expansion structure, and after further expanding to the nanomaterial, more interesting phenomena. For example, NPR has recently found NPR in carbon nanotubes and metal nano plates. In addition, the two-dimensional (2D) material such as graphene is expected to be applied to a variety of fields, and it has also achieved NPR through special projects, which can be cut into nano-belts, introduced to vacancy defects, and generate periodic porous and corrugation at extremely high temperatures. Bend, etc. But how the NPR mechanism of 2D materials is unclear.
Qin Guangzhao and Zhengzhou University of Hunan University, Qin Zhenzhen, based on the first principle of principles, collaborative research on new two-dimensional honeycombs such as graphene, silicon, H-BN, H-GaN, H-SiC and H-BAS The material responds under the single axis strain, predicting that the above materials are negative in the armchair direction. Although their elemental components are different, their NPR is increasingly increased by the key angle. The abnormal increase in this key angle cannot be explained through the viewpoint of the geometric structure and mechanical response of the traditional level (such as a classic molecular dynamics simulation based on the experience of the potential function). This work analyzes the change in key geometric parameters and track hybrid effects under stress regulation, which clarifies the anti-normal increase in key angle and the underlying physical mechanism of NPR from the electron structure level. This mechanism is also applicable to other nanostructures having NPR phenomena.
Negative Poisson's Ratio in Two-Dimensional Honeycomb Structure
Guangzhao qin and zhenzhen qin
Negative Poisson's ratio (NPR) in auxetic materials is of great interest due to the typically enhanced mechanical properties, which enables plenty of novel applications. In this paper, by employing first-principles calculations, we report the emergence of NPR in a class of two -dimensional honeycomb structures (graphene, silicene, h-BN, h-GaN, h-SiC, and h-BAs), which are distinct from all other known auxetic materials. They share the same mechanism for the emerged NPR despite the different chemical Composition, Which lies in the increased bond Angle (θ). However, the increase of θ is quite intriguing and anomalous, which can not be explained in the traditional point of view of the geometry structure and mechanical response, for example, in the framework of classical molecular dynamics simulations based on empirical potential. We attribute the counterintuitive increase of θ and the emerged NPR fundamentally to the strain-modulated electronic orbital coupling and hybridization. It is proposed that the NPR phenomenon can also emerge in other nanostructures or nanomaterials with similar honeycomb structure. The physical origin as revealed in our study deepens the understanding ON The NPR AND Woulder Shed Light on Future Design of Modern Nanoscale Electromechanical Devices with Special Functions Based on Auxetic Nanomaterials and Nanostructures.
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