Negative Piezoelectric Response in YS₂

The magnetic and piezoelectric properties of the YX₂ (X = S, Se and Te) monolayers have been investigated using first-principles calculations. The spin-polarized electronic band structures of both monolayer and bilayer systems were analyzed using the HSE hybrid functional and the conventional PBE + U approach. Our results show that the YS₂ monolayer adopts a 1H structure and exhibits a negative in-plane piezoelectric coefficient <i>d</i> ₁₁ = -2.53 × 10^-10 C/m. The substantial Born effective charge induces a negative response along the in-plane armchair direction. These findings reveal an intricate relationship between structural configurations and p-orbital ferromagnetism in transition-metal dichalcogenides, providing valuable insights for future exploration of piezoelectric materials.