Involvement of cationic sublattices in multiple polarization states in CuInP2S6 ferrielectrics

The contribution of copper and indium cationic sublattices on polarization hysteresis loops in CuInP2S6 van der Waals ferrielectrics has been studied within the quantum anharmonic oscillator model that considers the ordering dynamics of Cu+ cations in the double-well local potential and displacive dynamics of In3+ cations in the three-well shaped potential. The multiple polarization states are manifested as single, double, and triple P(E) hysteresis loops. The triple loops originate from a field-induced ferrielectric to ferroelectric phase transition within a certain range of the phase diagram with continuous increase in the spontaneous polarization below the second-order transition from the paraelectric phase to the ferrielectric state.