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.