Giant Photostriction Rate for Remote Opto-ultrasonic Structural Health Monitoring

Extending photocarrier lifetime, accelerating photostrictive strain buildup, and engaging more light–lattice interactions are key to improving bulk ferroelectric photostriction rate (coefficient integrating strain magnitude and generation speed, typically < 10⁻³ s⁻¹) for reliable remote ultrasound generation. We report non-poled terbium-doped (K,Na)NbO₃ ceramics (KNN-Tb), where Tb³⁺ 4 f -electron trapping prolongs photocarrier lifetime, enabling efficient carrier migration to domain walls for screening depolarization field. Hierarchical nanostructures—dense nanodomains (rapid local photostriction) and subwavelength grains (more light–lattice interactions and enhanced collective strain)—yield the photostriction rate of 6.41×10⁻¹ s⁻¹, two orders above conventional bulk ferroelectrics. Non-poled KNN-Tb avoids depoling issue, enabling robust opto-ultrasonic transducers that generate intense ultrasound under low-cost laser, demonstrated remote structural health monitoring. Our bulk ferroelectric design strategy enables cost-effective, high-performance remote opto-ultrasonic sensing technologies.