Monolayer group IV monochalcogenides T-MX (M = Sn, Ge; X = S, Se) with fine piezoelectric performance and stability

Abstract

Monolayer group monochalcogenides (MX; M = Sn, Ge; X = S, Se) in the orthogonal α-phase are excellent piezoelectric materials. In this study, a configuration with bonding features similar to the α-phase is proposed (T-phase) for monolayer MX using the first-principles method. Based on the modern theory of polarization, as implemented in Vienna Ab initio Simulation Package, the T-phase is determined to be an excellent piezoelectric phase for monolayer MX. The in-plane piezoelectric coefficient d11 of T-SnS is 452.3 pm/V, which is larger than that reported for most two-dimensional binary compounds in the α-phase, including α-SnSe (∼250 pm/V). The large piezoelectric coefficients of T-MX mainly stem from its distinctive puckered configuration, which make it extraordinarily flexible along the polarization direction. The study results suggest a possibility for designing high piezoelectric coefficient materials with MX, and the potential application of T-MX in the fields of energy collection and nanoelectromechanical systems needs to be analyzed in future studies.