Chemical Doping Engineering of Polarization and Topological Textures in van der Waals Ferroelectric CuInP₂S₆

Precise modulation of ferroelectric properties in van der Waals (vdW) layered materials is crucial for multifunctional nanoelectronics. Here, we demonstrate that Li⁺ substitution at Cu sites (Cu_1-xLi_xInP₂S₆, x≤ 0.1) concurrently enhances ferroelectric and ionic conductivities, and enriches the polarization configurations of CuInP₂S₆. With Li-doping, benefiting from the strengthened Cu-S interlayer bond and reduced interlayer spacing, the Curie temperature increases from 315 K (pristine) to 327 K (x = 0.1), and Cu⁺ ionic conductivity activation energy is lowered from ∼0.6 eV (pristine) to ∼0.4 eV (x = 0.1). Meanwhile, the high-polarization state is stabilized and gives rise to the coexistence of low- and high-polarization states (LP and HP), which lays a fertile ground for topological polar texture. Numerous polar bubbles and labyrinth domains with varied sizes and shapes are observed at the border between HP and LP phases. Interestingly, a strain gradient switches the HP to the LP state, establishing an intriguing flexoelectrical response and providing a mechanical pathway to tune and confine the polar texture. This work provides a feasible chemical strategy to modulate ferroelectric properties and polar configurations in vdW ferroelectrics, offering promising opportunities for advanced electronics, neuromorphic computing, and topotronics.