单层砷硫族化合物本征铁电性和大压电性的预测
Prediction of intrinsic ferroelectricity and large piezoelectricity in monolayer arsenic chalcogenides
摘要：
表现出自发电极化的强度的二维材料是功能材料的显著兴趣。然而，尽管理论上预测了许多二维极性材料，但实验证实的二维铁电体的数量仍然远远少于体铁电体。我们提供了强有力的证据表明，Pmn 2 $_1$相的砷硫属化物作为$_2$ X $_3$（X=S，Se，和Te），其中包括最近孤立的单层雌黄，是本征铁电体，并表现出很强的面内压电性。我们发现，计算的能量势垒集体扭转的电极化的强度或移动180 $^\circ$域壁是合理的，以前报道的铁电体相比。我们提出了一个高对称结构（Pmmn空间群）转变为铁电Pmn2 $_1$相的软B $_{2u}$声子模式。通过研究其他软模式的高对称性Pmmn结构，我们确定了几个未被发现的亚稳多晶型，包括极性相（与P2 $_1$空间群）具有相当大的压电性。
英文摘要：
Two-dimensional materials that exhibit spontaneous electric polarization are of notable interest for functional materials. However, despite many two-dimensional polar materials are predicted in theory, the number of experimentally confirmed two-dimensional ferroelectrics are still far less than bulk ferroelectrics. We provide strong evidence that the Pmn2$_1$ phase of arsenic chalcogenides As$_2$X$_3$ (X=S, Se, and Te), which include the recently isolated monolayer orpiment, are intrinsic ferroelectrics and demonstrate strong in-plane piezoelectricity. We found the calculated energy barriers for collectively reversing the electric polarization or moving a 180$^\circ$ domain wall are reasonable compared to previously reported ferroelectrics. We propose a high-symmetry structure (with Pmmn space group) transforms into the ferroelectric Pmn2$_1$ phase by a soft B$_{2u}$ phonon mode. By studying other soft modes of the high-symmetry Pmmn structure, we identify several undiscovered metastable polymorphs, including a polar phase (with a P2$_1$ space group) with sizable piezoelectricity.
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