Multiscale Simulations of Defect Dipole-Enhanced Electromechanical Coupling at Dilute Defect Concentrations

TL;DR

This study uses large-scale molecular dynamics simulations to reveal how defect dipoles enhance electromechanical coupling in ferroelectric BaTiO3, providing atomistic insights for improving ferroelectric device performance.

Contribution

It introduces a first-principles-based atomistic model to quantitatively link defect dipole characteristics with ferroelectric properties and electromechanical responses.

Findings

Small defect dipole concentration (0.1%) significantly enhances electromechanical response.

Orientation of defect dipoles relative to external field critically influences material behavior.

Defect dipole engineering can improve ferroelectric ceramics for sensors and actuators.

Abstract

The role of defects in solids of mixed ionic-covalent bonds such as ferroelectric oxides is complex. Current understanding of defects on ferroelectric properties at the single-defect level remains mostly at the empirical level, and the detailed atomistic mechanisms for many defect-mediated polarization-switching processes have not been convincingly revealed quantum mechanically. We simulate the polarization-electric field (P-E) and strain-electric field ({$\epsilon$}-E) hysteresis loops for BaTiO3 in the presence of generic defect dipoles with large-scale molecular dynamics and provide a detailed atomistic picture of the defect dipole-enhanced electromechanical coupling. We develop a general first-principles-based atomistic model, enabling a quantitative understanding of the relationship between macroscopic ferroelectric properties and dipolar impurities of different orientations, concentrations, and dipole moments. We find that the collective orientation of dipolar defects relative to the external field is the key microscopic structure feature that strongly affects materials hardening/softening and electromechanical coupling. We show that a small concentration (0.1 at.%) of defect dipoles dramatically improves electromechanical response. This offers the opportunity to improve the performance of inexpensive polycrystalline ferroelectric ceramics through defect dipole engineering for a range of applications including piezoelectric sensors, actuators, and transducers.