Structural, Mechanical, and Piezoelectric Properties of Janus Bidimensional Monolayers

In the present work, the noncentrosymmetric 2D ternary Janus monolayers Al2XX’(X/X’ = S, Se, Te and O), Si2XX’(X/X’ = P, As, Sb and Bi), and A2PAs(A = Ge, Sn and Pb) have been studied based on first-principles calculations. We find that all the monolayers exhibit in-plane d12, and out-of-plane d13 piezoelectric coefficients due to the lack of reflection symmetry with respect to the central A atoms. Moreover, our calculations show that Al2OX(T = S, Se, Te) chalcogenide monolayers have higher absolute in-plane piezoelectric coefficients. However, the highest out-of-plane values are achieved in the Si2PBi monolayer, larger than those of some advanced piezoelectric materials, making them very promising transducer materials for lightweight and high-performance piezoelectric nanodevices.