Engineering Ferroelectricity and Large Piezoelectricity in h-BN

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Hexagonal boron nitride (h-BN) is a centrosymmetric layered van der Waals material lacking spontaneous electric polarization.
• Its symmetric structure prevents intrinsic ferroelectric or piezoelectric properties.

Purpose of the Study:

• To investigate the effects of isovalent doping (Al, Ga) on the structural, ferroelectric, and piezoelectric properties of h-BN.
• To explore the potential of doped h-BN for electronic applications, particularly nonvolatile memories.

Main Methods:

• Extensive density functional theory (DFT) calculations were performed.
• Analysis focused on symmetry breaking, dipole moment induction, and structural stability.
• Ferroelectric polarization, switching barriers, and piezoelectric coefficients were computed.

Main Results:

• Doping with Al or Ga breaks inversion symmetry, inducing local dipole moments and promoting ferroelectricity.
• A 'protruded layered' structure is energetically favored for doping concentrations below 25%.
• Computed polarization values (7.227–21.117 μC/cm²) and switching barriers (16.684–45.838 meV/atom) are comparable to known ferroelectrics.
• Doping induces a significant negative piezoelectric response (e.g., d₃₃ of -24.214 pC/N for Ga-doped h-BN).
• Ferroelectricity persists down to the trilayer limit.

Conclusions:

• Isovalent doping of h-BN can effectively induce ferroelectric and piezoelectric properties.
• The resulting material exhibits promising characteristics for applications in ferroelectric nonvolatile memories.
• The layered structure and low elastic constant C₃₃ contribute to the large piezoelectric response.