Piezoelectricity is pivotal for applications in micro/nanoelectromechanical systems (MEMS/NEMS). Inducing such a property in 2D systems via the reduction of the dimensionality of their corresponding 3D bulk is here explored. Based on DFT theory and Gaussian-type-localized basis sets, the structural, electronic, mechanical, and piezoelectric properties of both 3D and 2D rare earth monochalcogenides RmX (Rm = Tm, Yb, Lu, and X = S, Se, Te) are investigated using the CRYSTAL code. Most intriguingly, the 2D LuX compounds display a buckled structure, where the Lu and X atoms protrude from the monolayer surface leading to an additional out-of-plane piezoelectric effect; (e₃₁ = 2 104.84, 1 770.28, 1 689.79 pC/m, and d₃₁ = 56.37, 49.76, and 147.90 pm/V for LuS, LuSe, and LuTe, respectively). Such piezoelectric response is two orders of magnitude larger than the one of recently reported 2D ferroelectric MXenes, and is nearly thirty times larger than the commonly used AlN and GaN bulk structures. Furthermore, the reduced elastic constants obtained, when compared to other 2D materials, confirm the flexibility and softness of the considered 2D systems.

压电对于微/纳米机电系统 (MEMS/NEMS) 中的应用至关重要。此处探讨了通过减少相应 3D 体积的维数在 2D 系统中引入这种特性。基于 DFT 理论和高斯型局部基组，3D 和 2D 稀土单硫族化合物 RmX（Rm = Tm、Yb、Lu 和 X = S、Se、Te）的结构、电子、机械和压电特性使用 CRYSTAL 代码进行调查。最有趣的是，二维 LuX 化合物显示出弯曲结构，其中 Lu 和 X 原子从单层表面突出，导致额外的面外压电效应；( e ₃₁  = 2 104.84, 1 770.28, 1 689.79 pC/m, d ₃₁ = LuS、LuSe 和 LuTe 分别为 56.37、49.76 和 147.90 pm/V）。这种压电响应比最近报道的二维铁电 MXenes 大两个数量级，比常用的 AlN 和 GaN 块状结构大近 30 倍。此外，与其他二维材料相比，所获得的弹性常数降低，证实了所考虑的二维系统的柔韧性和柔软性。