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

## TL;DR

This paper shows how adding lithium to a 2D material enhances its electric properties and creates complex polarization patterns, which could be useful for advanced electronics.

## Contribution

The study introduces Li⁺ doping as a chemical strategy to modulate polarization and generate topological textures in a van der Waals ferroelectric material.

## Key findings

- Li⁺ doping increases Curie temperature and enhances ionic conductivity in CuInP2S6.
- High- and low-polarization states coexist, leading to topological polar textures like bubbles and labyrinth domains.
- Strain gradients induce a flexoelectric response, enabling mechanical control of polarization states.

## Abstract

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 (Cu1‐xLixInP2S6, 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.

Our work reports that Li⁺ doping in CuInP2S₆ induces coexistence of high‐ and low‐polarization states, which fosters a rich spectrum of topological polar textures, such as bubbles and labyrinth domains. An unconventional flexoelectric effect is also discovered, where strain gradients can mechanically manipulate these polarization states and their topological features.