Ordering/displacive ferrielectricity in 2D CuInP₂S₆

Abstract

Using DFT-based molecular dynamics simulation of Cu⁺ cations flipping and In³⁺ cations displacive dynamics, we clarify the dipole ordering of CuInP₂S₆ ferrielectrics through the second order Jahn-Teller effect which determines the double-well potential for copper cations as well as three-well potential for indium cations inside the structural layers. The temperature dependence of the spatial distribution of Cu⁺ and In³⁺ cations is also described within the quantum anharmonic oscillator model. In³⁺ cations play a decisive role in the character of the polar ordering: at ambient or for positive pressures, the first order transition occurs; with the rise of negative compression, the ferrielectric transition evolves to the second order. The peculiarities of spontaneous polarization switching are related to the contributions of copper and indium cationic sublattices.

Keywords:

• CuInP₂S₆
• ferrielectric states
• polarization
• cationic contributions

Disclosure statement

No potential conflict of interest was reported by the authors.