Electronic, Mechanical, Vibrational and Piezoelectric Properties of Mg3X2 (X = As, Sb) Monolayers

Abstract

Recently, bulk Mg₃X₂ (X = As, Sb) have been intensively studied for their unique properties for thermoelectric use. However, studies on their two-dimensional counterparts are not sufficient. In this work, we systematically investigated the electronic, mechanical, vibrational, and piezoelectric properties of Mg₃X₂ (X = As, Sb) monolayers. The results indicate that both monolayers have negative formation energies with dynamical and mechanical stability. Mg₃As₂ monolayer is a narrow band gap semiconductor, while Mg₃Sb₂ monolayer is an indirect one. The origin of the band structure was revealed by the calculated partial density of states. The bonding property of both monolayers was analyzed by different methods. Elastic constants were obtained by density functional perturbation theory, and the related physical quantities were derived and analyzed. In-plane strengths along the zigzag and armchair directions of both materials were calculated, and the fracture mechanisms were uncovered. The vibrational modes at the Brillouin center were classified through group theory analysis, and the corresponding eigenvectors and frequencies were calculated and presented. Infrared vibrational spectra were simulated, and the reason for the vanishment of some infrared peaks was disclosed. Piezoelectric and dielectric coefficients were also computed and discussed.