Henan Provincial Key Laboratory of Nanocomposites and Applications, Institute of Nanostructured Functional Materials, Huanghe Science and Technology College, Zhengzhou 450006, China.
Phys Chem Chem Phys. 2018 Jul 18;20(28):18924-18930. doi: 10.1039/c8cp01353e.
Auxetic materials have numerous promising engineering applications such as fracture resistance and energy storage due to their negative Poisson's ratios (NPRs). However, compared to materials possessing positive Poisson's ratios (PPRs), auxetic materials are rare. In this paper, by employing first principles calculations, we found a high NPR two-dimensional (2D) material, tungsten carbide (W2C), in the transition metal carbides (MXenes). Our results of the relatively moderate Young's modulus and fracture strength as well as the critical strain showed that the 2D monolayer W2C is an extraordinary flexible material. Our DFT results also demonstrated that W2C possesses high NPRs while Hf2C and Ta2C have PPRs. Furthermore, the mechanically induced deformation mechanism and the NPR formation mechanism of W2C have been proposed. Such an intrinsic NPR in W2C is attributed to the strong coupling between the C-p and W-d orbitals in the pyramid structural unit. The mechanically induced deformation mechanism and the PPR formation mechanism of Hf2C have also been determined. The intrinsic NPR for W2C transforms to PPR upon the surface functionalization induced. The behavior occurs due to the W-C interaction weakening. The excellent NPR in the 2D MXene material combined with other outstanding properties such as the metallic state would bring about its promising engineering prospects, ranging from the metal-ion battery, to automobiles and aircraft.
具有负泊松比（NPR）的超弹性材料由于其在抗断裂和能量存储等方面具有众多有前景的工程应用。然而，与具有正泊松比（PPR）的材料相比，超弹性材料较为少见。在本文中，通过使用第一性原理计算，我们在过渡金属碳化物（MXenes）中发现了一种具有高 NPR 的二维（2D）材料——碳化钨（W2C）。我们得到的相对适中的杨氏模量和断裂强度以及临界应变表明，2D 单层 W2C 是一种非凡的柔性材料。我们的 DFT 结果还表明，W2C 具有高 NPR，而 Hf2C 和 Ta2C 具有 PPR。此外，还提出了 W2C 的机械诱导变形机制和 NPR 形成机制。W2C 中的这种固有 NPR 归因于在金字塔结构单元中 C-p 和 W-d 轨道之间的强耦合。还确定了 Hf2C 的机械诱导变形机制和 PPR 形成机制。W2C 的固有 NPR 在表面官能化诱导下会转变为 PPR。这种行为是由于 W-C 相互作用减弱所致。2D MXene 材料具有出色的 NPR 和其他优异性能，如金属态，这将为其带来广阔的工程应用前景，涵盖了从金属离子电池到汽车和飞机等领域。
