Low-dimensional ferroelectrics are highly desired for applications and contain exotic physics. Here a functionalized MXene ${\mathrm{Hf}}_2{\mathrm{CF}}_2$ monolayer is theoretically studied which manifests a nonpolar to polar transition upon moderate biaxial compressive strain. Accompanying this structural transition, a metal-semiconductor transition occurs. The in-plane shift of the unilateral fluorine layer leads to a polarization pointing out-of-plane. Such ferroelectricity is unconventional, similar to the recently proposed interlayer-sliding ferroelectricity but not identical. Due to its specific hexapetalous potential energy profile, the possible ferroelectric switching paths and domain walls are nontrivial, which are mediated via the metallic paraelectric state. In this sense, the metallic walls can be manipulated by reshaping the ferroelectric domains.

中文翻译：

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应变 Hf2CF2 单层中的铁电性

低维铁电体在应用中非常受欢迎，并且包含奇异的物理特性。这是一个功能化的 MXene${\mathrm{高频}}_2{\mathrm{CF}}_2$理论上研究了单层，它在中等双轴压缩应变下表现出非极性到极性的转变。伴随这种结构转变，发生了金属-半导体转变。单边氟层的面内位移导致指向面外的极化。这种铁电性是非常规的，类似于最近提出的层间滑动铁电性，但不完全相同。由于其特定的六瓣势能分布，可能的铁电开关路径和畴壁是非常重要的，它们通过金属顺电态进行调节。从这个意义上说，可以通过重塑铁电畴来操纵金属壁。