Out-of-Plane Piezoelectricity of V2CXY (X/Y = O, S, Se) MXenes Monolayers for Wearable Devices

Due to the characteristics of two-dimensional materials, they have demonstrated unique advantages in fields such as piezoelectric devices. Unfortunately, most piezoelectric materials currently do not simultaneously possess excellent piezoelectric effects and mechanical properties. Since the emergence of MXenes, their excellent electrical conductivity and good dynamic and mechanical stability have garnered widespread attention in the energy storage field. Consequently, MXenes are also considered candidates for piezoelectric materials. In this study, the piezoelectric properties and mechanical stability of V2CXY (V2COS, V2CSO, V2COSe, V2CSeO) MXenes monolayers were predicted using first-principles methods based on density functional theory. The results indicate that these four materials exhibit good dynamic, thermodynamic, and mechanical stability. It is noteworthy that due to the structural inversion asymmetry and differences in electronegativity, the structure exhibits strong in-plane piezoelectric effects and excellent out-of-plane piezoelectric effects. In particular, the d 33 piezoelectric strain coefficient is 2 to 3 orders of magnitude higher than d 22 and d 31, with the d 33 coefficient of V2CSO reaching up to 313.01 pm/V. This makes these materials highly promising for potential applications in wearable and piezoelectric devices.