The graphenelike form of carbon nitride is known as 𝑔−C3⁢N4, a single sheet of which may be composed of an 𝑠-triazine (𝑆-type) or tri-𝑠-triazine (𝑇-type) periodic lattice with a different size of hole. By employing the first-principles calculation, we find that the difference in the out of plane polarization caused by the symmetry breaking of the 𝑆-type or 𝑇-type structure of bilayer 𝑔−C3⁢N4 through interlayer sliding may be related to the size of the in-plane hole. The nonpolar bilayer 𝑔−C3⁢N4 (𝑆- or 𝑇-type) state needs to slide about two bond lengths before it is electrically driven to the polar state, resulting in ferroelectric structures with opposite polarization directions. It has been confirmed experimentally and theoretically [Zelisko et al., Nat. Commun. 5, 4284 (2014)] that the anomalous piezoelectric properties of 𝑇-type 𝑔−C3⁢N4 monolayer come from their noncentrosymmetric triangular holes. Interestingly, we find here that the 𝑆-type 𝑔−C3⁢N4 exhibits the opposite piezoelectric property to the 𝑇-type 𝑔−C3⁢N4, that is, a negative longitudinal piezoelectricity (NLP). Our computational analysis shows that the superposition of two reversed triangular holes in the 𝑆-type 𝑔−C3⁢N4 plane will result in the emergence of NLP. Hence, the origin of different piezoelectric properties between 𝑆-type and 𝑇-type 𝑔−C3⁢N4 is comparatively elucidated. These results provide alternative structural manipulation degrees of freedom for the inherent properties of two-dimensional van der Waals layered semiconductor materials, and expand ferroelectric candidate materials for next-generation nanoelectronic devices.

中文翻译：

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双层和三层中的面内滑动铁电性和压电性g−C3N4


氮化碳的石墨烯状形式称为 g-C3N4，其单片可能由具有不同空穴大小的 s-三嗪（S 型）或三-s-三嗪（T 型）周期晶格组成。通过采用第一性原理计算，我们发现双层 g-C3N4 的 S 型或 T 型结构通过层间滑动对称性破裂引起的面外极化差异可能与面内孔的大小有关。非极性双层 g-C3N4（S 型或 T 型）状态在被电驱动到极性状态之前需要滑动大约两个键长，从而产生具有相反极化方向的铁电结构。它已经在实验和理论上得到证实 [Zelisko et al.， Nat. Commun.5， 4284 （2014）] T 型 g-C3N4 单分子层的反常压电特性来自其非中心对称三角形空穴。有趣的是，我们在这里发现 S 型 g-C3N4 表现出与 T 型 g-C3N4 相反的压电特性，即负纵向压电 （NLP）。我们的计算分析表明，在 S 型 g-C3N4 平面上两个反向三角形孔的叠加将导致 NLP 的出现。 因此，相对阐明了 S 型和 T 型 g-C3N4 之间不同压电性质的起源。这些结果为二维范德华分层半导体材料的固有特性提供了替代的结构操纵自由度，并为下一代纳米电子器件扩展了铁电候选材料。