Lattice dynamics of piezoelectric response of 2D Janus Y2Se2IF under strain

Two-dimension (2D) Janus materials with asymmetric atomic structure have been found to have unique intrinsic vertical polarization properties, where an electron is more likely to deviate from the neutral center and make a greater contribution to the dipole moment. Here, based on the calculation of the piezoelectric properties of ten types of 2D Janus materials, we identify the sole material Y2Se2IF, where the contribution of internal-strain piezoelectricity plays a dominant role. We further conduct a lattice dynamics analysis of its piezoelectric properties and find that the A1(6) (9.313 THz) mode contributes 73% of the internal-strain piezoelectric component e31i, resulting from the large mode polarity and large phonon–strain coupling. The electronic structure indicates that this significant mode contribution comes from high bond ionicity, large electronegativity differences, and the effective regulation of bond length by modal factors. We further analyze the evolution of the piezoelectric components, phonon mode contributions, atomic contributions, mode polarity, and phonon–strain coupling of the piezoelectricity of the Y2Se2IF under biaxial strain. The results show that strain leads to an enhancement of phonon–strain coupling, resulting in a significant fluctuation in the piezoelectric contribution of the A1(6) mode. These dynamic analyses of the piezoelectric properties provide a theoretical basis for the application of 2D Janus materials in the field of piezoelectrics.