Giant photostriction rate for remote opto-ultrasonic structural health monitoring

Extending photocarrier lifetime, accelerating photostrictive strain buildup, and engaging more light–lattice interactions are essential to increase the bulk photostriction rate—a key figure of merit integrating strain magnitude and generation speed (typically < 10⁻³ s⁻¹ in bulk ferroelectrics)—for efficient remote ultrasound generation. Here, we report non-poled terbium-doped (K,Na)NbO₃ ceramics, where Tb³⁺ 4f-electron trapping prolongs photocarrier lifetime, enabling efficient carrier drift to domain walls for screening depolarization field. Hierarchical nanostructures—dense nanodomains (accelerating photostriction via coupled local bulk photovoltaic and converse piezoelectric effects) and subwavelength grains (more light–lattice interactions and enhancing collective photostriction)—yield an outstanding bulk photostriction rate of 6.41×10⁻¹ s⁻¹, two orders above conventional bulk ferroelectrics. Non-poled ceramics avoid depoling issue, enabling robust and low power opto-ultrasonic transducers for reliable remote structural health monitoring. Our bulk ferroelectric design strategy enables cost-effective, high-performance opto-ultrasonic sensing technologies.