Prediction of the ferroelastic and negative Poisson’s ratio of a two-dimensional α-CaX (X = S, Se) monolayer
School of Science, Wuhan University of Technology, 430070, Wuhan, People’s Republic of China
2 Research Center of Materials Genome Engineering, Wuhan University of Technology, 430070, Wuhan, People’s Republic of China
Accepted: 18 July 2022
Published online: 7 August 2022
Two-dimensional ferroelastic semiconductor materials have attracted wide attention due to their unique properties. Along these lines, in this work, a series of new types of two-dimensional materials called monolayer α-CaX (X = S, Se) were proposed and thoroughly investigated by performing first-principles calculations. Different from the hexagonal lattice structure of β-CaX that was previously reported, the α-CaX structure holds a tetragonal lattice. By considering the calculated phonon spectra and the respective Born criteria, good stability was demonstrated for the α-CaX monolayer. The values of 3.41 eV (α-CaS) and 3.11 eV (α-CaSe) were calculated for the indirect band gap of the α-CaX (X = S, Se) structures, respectively. The mechanical properties of the proposed α-CaX monolayer were proved to exhibit distinct anisotropy.Particularly,the existence of a negative Poisson’s ratio was detected for the case of α-CaSe. Additionally, strong ferroelastic signal and moderate energy barriers were found for both monolayer α-CaS and α-CaSe. All these intriguing properties render the α-CaX structures quite promising candidates for applications in shape memory devices and impact resistance materials.
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