Two-dimensional violet phosphorene (VP) nanosheets are promising semiconductor materials with unique cross structures distinct from those of their allotropes such as black phosphorene and blue phosphorene, but their mechanical behaviors remain almost unexplored. By using the first-principles calculations, in this paper we investigate the mechanical behaviors of monolayer, bilayer, and bulk VP under uniaxial tension. A phase transformation from the open-pore phase to closed-pore phase is observed in VP structures when under a specific tensile strain. It is revealed that the phase transformation is attributed to the competition between the rotation and elongation of sub-nano rods in VP structures during the loading process. Due to the phase transformation, the in-plane Poisson's ratio of monolayer VP can become greater than 1.2, while the bulk VP possesses a negative out-of-plane Poisson's ratio with a magnitude up to -0.3 at a certain strain. These results indicate that Poisson effects in VP are superior to those in any other existing two-dimensional materials. In addition, based on the tensor analysis of elastic constants, a strong mechanical anisotropy is observed in VP structures both before and after the phase transformation. Besides the mechanical properties, the band gap of all VP structures decreases as the applied tensile strain increases, which can eventually transform into the metallic state prior to their fracture. The combination of unique phase transformation, anomalous Poisson effect, strong mechanical anisotropy and tunable electronic properties render VP be a novel nanoscale metamaterial with multifunctional applications.

二维紫磷烯 (VP) 纳米片是一种很有前途的半导体材料，具有独特的交叉结构，不同于它们的同素异形体，如黑色磷烯和蓝色磷烯，但它们的机械行为几乎仍未被探索。通过使用第一性原理计算，本文研究了单层、双层和块体 VP 在单轴张力下的力学行为。当在特定的拉伸应变下，在 VP 结构中观察到从开孔相到闭孔相的相变。结果表明，相变归因于加载过程中VP结构中亚纳米棒的旋转和伸长之间的竞争。由于相变，单层VP的面内泊松比可以变得大于1.2，而体积VP具有负的面外泊松比，在一定应变下幅度高达-0.3。这些结果表明，VP 中的泊松效应优于任何其他现有二维材料中的泊松效应。此外，基于弹性常数的张量分析，VP结构在相变前后均观察到强烈的机械各向异性。除了机械性能外，所有 VP 结构的带隙随着施加的拉伸应变的增加而减小，最终可以在断裂前转变为金属状态。独特的相变、异常泊松效应、强机械各向异性和可调电子特性的结合使 VP 成为具有多功能应用的新型纳米级超材料。