Tunable quadruple-well ferroelectric van der Waals crystals

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid-State Chemistry

Background:

• Layered thio- and seleno-phosphates are explored as dielectrics for 2D electronic materials.
• Understanding ferroelectric properties in these materials is crucial for next-generation electronics.

Purpose of the Study:

• To predict and verify unusual ferroelectric properties in copper indium thiophosphate (CuInP2S6).
• To investigate the influence of strain on ferroelectric behavior and piezoelectric coefficients.

Main Methods:

• Density functional theory (DFT) calculations.
• Quantum molecular dynamics (QMD) simulations.
• Variable-temperature, -pressure, and -bias piezoresponse force microscopy (PFM).

Main Results:

• Discovery of a uniaxial quadruple potential well for copper (Cu) displacements in CuInP2S6.
• Strain significantly influences the potential energy landscape and negative piezoelectric coefficient.
• Experimental verification of four coexisting polarization states and their temperature-, pressure-, and bias-dependent behavior.

Conclusions:

• CuInP2S6 is a rare example of a uniaxial multi-well ferroelectric.
• The unique ferroelectric properties offer potential for novel data storage and electronic devices.
• Further fundamental studies and application development are warranted.