Interlayer Slip Engineering Induces Unexpected Out-Of-Plane Piezoelectricity in Group-VA Nanosheets

Piezoelectricity, arising from inversion symmetry breaking, is generally forbidden in centrosymmetric β-phase bismuth (Bi) and antimony (Sb) structures. Here, we experimentally demonstrate a previously unreported out-of-plane piezoelectricity in β-phase Bi and Sb nanosheets synthesized via electrochemical exfoliation. Piezoresponse force microscopy (PFM) and second-harmonic generation (SHG) measurements confirm the strong piezoelectric response with a longitudinal coefficient (d₃₃) up to ∼200 pm V^-1, comparable to or exceeding that of conventional 2D piezoelectric materials. Density functional theory (DFT) calculations reveal that interlayer slip during exfoliation induces a transition from AA- to AB-stacking, effectively breaking inversion symmetry and leading to large out-of-plane polarization. This discovery introduces a universal mechanism to generate piezoelectricity in non-piezoelectric 2D materials through stacking-mode engineering, providing opportunities for nanoscale electromechanical and piezocatalytic devices.