Dynamic strain-gradient-induced polarization and nonlinear electromechanical coupling in noncentrosymmetric quantum oxide crystals
DOI:
https://doi.org/10.54355/tbusphys/4.1.2026.0046Keywords:
strain-gradient polarization, nonlinear electromechanical coupling, dynamic dielectric response, noncentrosymmetric oxide crystals, second-harmonic susceptibility, finite-element modelingAbstract
This study investigates dynamic strain-gradient-induced polarization and nonlinear electromechanical coupling in a noncentrosymmetric wide-bandgap oxide single crystal. The objective was to experimentally verify enhanced dynamic polarization mechanisms beyond classical flexoelectric descriptions and to correlate the results with continuum-level numerical modeling. High-quality single crystals were structurally verified by X-ray diffraction, followed by dynamic polarization measurements over a frequency range from 10 Hz to 1 MHz. Controlled strain gradients were introduced via three-point bending, and nonlinear susceptibility was extracted using harmonic analysis. Finite-element simulations were performed to reproduce spatial polarization distributions under identical boundary conditions. The polarization amplitude exhibited a low-frequency plateau of approximately 4.8 µC/m² and decreased to 3.48 µC/m² at 1 MHz, indicating dispersive dynamic behavior. Under applied strain gradients up to 3 × 10³ m⁻¹, polarization increased from 4.76 µC/m² to 7.81 µC/m², demonstrating nearly linear scaling with higher-order enhancement at larger gradients. A quadratic nonlinear response was confirmed, with second-harmonic polarization reaching 2.052 µC/m² at 100 kV/m. Temperature variation from 20 K to 400 K produced monotonic damping without phase-transition anomalies. Numerical modeling reproduced experimental amplitudes and revealed pronounced spatial localization of polarization. The results confirm robust dynamic electromechanical coupling exceeding classical continuum expectations and establish strain-gradient-driven polarization as a stable and tunable mechanism in noncentrosymmetric quantum crystals. The investigated material was wurtzite ZnO (P6₃mc) with a direct bandgap of approximately 3.3–3.4 eV at room temperature.
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