In this work, we studied the stability and ferroelectricity of two-dimensional (2D) group-IV monochalcogenides MX (M = Ge, Sn, or Pb; X = S, Se, or Te).
在這項工作中，我們研究了二維（2D）IV族單硫化物MX（M = Ge，Sn或Pb; X = S,Se或Te）的穩定性和鐵電性。
Two competing crystal structures of these 2D compounds have been considered, including the rippled crystal structure with a space group of Pmn21,which can be obtained from exfoliation, and the P3¯m1 hexagonal crystal structure containing the X-M-M-X building blocks.
這些二維化合物具有兩種相互競爭的晶體結構，包括具有Pmn21空間群的波紋晶體結構（可剝離獲得）和 P3¯m1六方晶體結構（含有X-M-M-X結構單元）。
We find that the total energies of the rippled phases of PbX, SnS and SnSe are lower than those of the corresponding hexagonal phases; particularly, the rippled phases of SnS and SnSe exhibit spontaneous
polarizations and ferroelectricity.
我們發現PbX，SnS和SnSe的波紋相的總能量低於相應六方相的總能量;特別是SnS和SnSe的波紋相呈現自發極化和鐵電性。
On the other hand, the hexagonal phases of GeX and SnTe are energetically more stable than the corresponding rippled phases; because the hexagonal phases are centrosymmetric, these 2D compounds are non-ferroelectric.
另一方面，GeX和SnTe的六方相在能量上比相應的波紋相更穩定;因為六方相是中心對稱的，所以這些二維化合物是非鐵電的。
To engineer the ferroelectricity of 2D group-IV mono chalcogenides, we have investigated the effects of alloying and equibiaxial strain.
為了設計二維IV族單硫化物的鐵電性，我們研究了合金化和等軸應變的影響。
Based on density functional theory calculations, we find that the rippled phases of GeX and SnTe can be stabilized via Pb alloying to achieve ferroelectricity.
基於密度泛函理論計算，我們發現Pb合金化可以穩定GeX和SnTe的波紋相從而實現鐵電性。
In addition, itis also found that equibiaxial tensile strain gives rise to ferroelectricity in the rippled phases of 2D PbX compounds.
此外，我們還發現等軸拉伸應變在二維PbX化合物的波紋相中會引發鐵電性。