Piezoelectricity in Monolayer and Multilayer Ti₃C₂Tx MXenes: Implications for Piezoelectric Devices

Piezoelectricity of two-dimensional (2D) materials with a noncentrosymmetric atomic structure is important to be studied and can be widely applied in many areas. Ti3C2Tx, as a kind of MXene, is able to be modified with functional groups and loses its central symmetry. Here, the mechanical-piezoelectric coupling equations of the Ti3C2Tx MXene with narrow band gaps are proposed to reveal the origin of piezoelectricity in monolayer Ti3C2Tx MXene. The multilayer 2D structure presents the extraordinary piezoelectric properties of the Ti3C2Tx MXene. Then, the modulation of the Schottky barrier by continuous piezoelectric potential distribution in Ti3C2Tx MXene and the nonuniform distribution of piezoelectric potential between unique polyatomic layer structures are described through the establishment of theoretical model, which explains the origin of the high conversion efficiency. Finally, the piezoelectric effect in multilayer Ti3C2Tx MXene as the circular piezoelectric resonator is analyzed. It is believed that the establishment of the atomic piezoelectric polarization model provides a solid foundation for understanding the piezoelectric mechanism in the Ti3C2Tx MXene and the preparation of piezoelectric devices such as a piezoelectric tactile sensor system, piezoelectric nanogenerator, and nanopiezoelectric resonator.