Ab initiostudy of flexoelectricity in MXene monolayers

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Flexoelectricity, the strain-gradient-induced polarization, is a universal electromechanical coupling effect in dielectrics.
• MXene monolayers, a novel class of 2D materials, offer unique electronic and mechanical properties.
• Understanding flexoelectricity in MXenes is crucial for designing next-generation electronic devices.

Purpose of the Study:

• To computationally investigate the flexoelectric properties of a wide range of MXene monolayers.
• To determine the transverse flexoelectric coefficients for 126 distinct MXene compositions.
• To analyze the influence of material composition and structural parameters on flexoelectricity.

Main Methods:

• First-principles calculations based on Kohn-Sham density functional theory (DFT).
• Computation of transverse flexoelectric coefficients along principal crystallographic directions.
• Calculation of mechanical bending modulus for normalization.

Main Results:

• Flexoelectric coefficients vary significantly across MXene monolayers, ranging from 0.19e to 1.3e.
• Nitride-based MXenes exhibit substantially larger flexoelectric coefficients compared to carbide-based counterparts.
• Flexoelectric response is nearly isotropic with respect to bending direction.
• Coefficients increase with structural thickness, but decrease when normalized by bending modulus.

Conclusions:

• MXene monolayers possess tunable flexoelectric properties with potential for electromechanical applications.
• The transition metal element is a key determinant of the flexoelectric response in MXenes.
• Thickness and mechanical stiffness are critical factors influencing the effective flexoelectricity of MXene monolayers.