Giant Shear-vertical Wave Bandgaps Induced by Diffuse Domain-walls in Ferroelectrics

Abstract

Diffuse domain walls are found to have a significant impact on the dielectric, piezoelectric, and thermal conductivity properties of ferroelectric materials. However, the influence of diffuse domain walls on the acoustic properties of ferroelectric materials has not yet been explored. In this work, we develop a phase-field perturbation model for ferroelectric materials and demonstrate that 90° diffuse domain walls can induce giant bandgaps of shear-vertical wave in bulk ferroelectrics. These giant bandgaps stem from the frequency-independent negative shear modulus localized at diffuse domain walls between adjacent domains. The bandgaps can be tuned by adjusting the periodic domain width, and the size dependence of the vibration frequency at the bandgap edges is consistent with experimental observations. Further transient dynamics analysis demonstrates that diffuse domain walls behave as freely sliding interfaces, which block the free propagation of shear-vertical waves and allow only resonant modes within a specific frequency range. The present work not only reveals the profound impact of diffuse domain walls on the propagation of elastic waves in ferroelectrics but also provides a theoretical framework for designing active and tunable sub-THz acoustic metamaterials based on ferroelectric periodic domain structures.