Poisson's ratio in the all-inorganic perovskite monolayers.

Poisson's ratios of two-dimensional (2D) all-inorganic perovskites Cs2PbX4 (X = Cl, Br, I) have been calculated by the first-principles calculations. The contribution of each geometric parameter (bond length L , bond angle Φ , rotation angle 𝜃 1 , and tilt angle 𝜃 2 ) to Poisson's ratio is obtained analytically. Through a comprehensive analysis of the geometric deformations of the perovskite under the uniaxial strain, we find that Poisson's ratios of the perovskites are sensitive to the change of the bond length L and the bond angle Φ. In addition, the value of the bond angle Φ 0 in the strain-free structure mainly determines the high in-plane anisotropy of Poisson's ratios in Cs2PbX4. [ABSTRACT FROM AUTHOR]