Shear-strain gradient induced polarization reversal in ferroelectric BaTiO_3 thin films: A first-principles total-energy study

摘要

Based on the first-principles total-energy calculation, we have studied the shear-strain gradient effect on the polarization reversal of ferroelectric BaTi03 thin films. By calculating the energies of double-domain supercells for different electric polarization, shear-strain gradients, and domain-wall displacement, we extracted, in addition to the domain-wall energy, the polarization energy, elastic energy, and flexoelectric coefficient of a single domain. The constructed Landau-Devonshire phenomenological theory yields a critical shear-strain gradient of 9.091 × 10~7/m (or a curvature radius (R) of 110 A) for reversing the 180° domain at room temperature, which is on the same order of the experimentally estimated value of 3.333 × 10~7/m (R = 300 A). In contrast to the commonly used linear response theory, the flexoelectric coefficient derived from fitting the total energy to a Landau-Devonshire energy functional does not depend on the specific pseudopotential. Thus, our method offers an alternative numerical approach to study the flexoelectric effect.