Van der Waals force-induced intralayer ferroelectric-to-antiferroelectric transition via interlayer sliding in bilayer group-IV monochalcogenides

Two-dimensional materials with ferroelectric properties break the size effect of conventional and unlock unprecedented potentials ferroelectric-related application at small length scales. In this work, using density functional theory (DFT) calculations, we discover a tribo-ferroelectricity behavior in group bilayer group-IV monochalcogenides (MX, M = Ge, Sn X S, Se). Upon interlayer sliding over an in-plane unit cell length, top layer exhibits reversible intralayer switching, leading to transition between (electric polarization 40$\mu$C/cm$^2$) antiferroelectric states MXs. Our results show that van der Waals interaction, which is usually considered be weak, can actually generate lattice distortion thus cause breaking/forming covalent bonds layer, observed phenomenon. This unique property has several advantages for energy harvesting existing piezoelectric triboelectric nanogenerators. The sliding-induced change as high 40$\mu$C/cm$^2$, open-circuit voltage two orders magnitude higher than MoS$_2$-based occurs time period unit-cell ultrahigh changing rate short-circuit current. theoretical prediction power output tribo-ferroelectric MXs moderate speed 1 m/s four MoS$_2$ nanogenerator, indicating great applications.