Effect of flexoelectricity on the acoustic property of ferroelectric materials—A phase field perturbation study

The flexoelectric effect, namely, the coupling between strain gradients and polarization, plays an important role in regulating the static domain structures of ferroelectric materials. However, its influence on the dynamic acoustic properties of ferroelectric materials and the underlying mechanisms remain to be elucidated. This work systematically investigates the influence of flexoelectricity on the acoustic dispersion relations of the prototypical ferroelectric PbTiO3 by incorporating the flexoelectric coupling energy into the phase-field perturbation model. The results indicate that the flexoelectric effect has a negligible influence on the acoustic dispersion curves of single-domain ferroelectrics. In multidomain ferroelectrics, the pronounced flexoelectric effect at domain walls causes the stiffening of domain structures and induces mode coupling between longitudinal and shear vertical waves, thereby generating bandgaps in acoustic dispersion curves. Furthermore, it is found that the width of bandgaps increases when the flexoelectric coefficient increases. The present study reveals the crucial role of the flexoelectric effect in the dynamic acoustic behavior of ferroelectrics, providing a new theoretical basis for the design of novel low-frequency acoustic/ultrasonic devices.