Ternary Penta-CoXS (X = Se and Te): 2D Monolayers with Coexistence of Antiferromagnetic, Auxetic, Photocatalytic, and Piezoelectric Features

Two-dimensional (2D) materials exhibit diverse properties, such as auxetic properties, magnetism, excellent photocatalytic performance, and unique piezoelectric response. However, the coexistence of these characteristics is rare in traditional 2D structures. Here, we propose 2D ternary pentagonal transition metal sulfides, namely, penta-CoXS (X = Se and Te), which exhibit coexistence of antiferromagnetic, auxetic, photocatalytic, and piezoelectric features. Our calculations demonstrate that penta-CoXS (X = Se and Te) monolayers possess robust thermodynamical, dynamical, and mechanical stabilities. Moreover, they are antiferromagnetic semiconductors with band gaps of 1.30 and 1.10 eV for CoSeS and CoTeS monolayers, respectively, corresponding to the Néel temperature (TN) of 325 and 110 K by Monte Carlo simulations. Both monolayers present suitable band edge positions for photocatalyzing water splitting, impressive electron and hole mobilities, and excellent visible light absorption. Besides, both display outstanding piezoelectric properties because of the broken inversion symmetry. These intriguing and multifunctional properties reveal the potential of CoXS (X = Se or Te) monolayers in versatile applications of nanoelectronics, optoelectronics, mechanics, photocatalysts, and piezoelectric devices.