Ultra-large electric field-induced strain in potassium sodium niobate crystals

Electromechanical coupling in piezoelectric materials allows direct conversion of electrical energy into mechanical energy and vice versa. Here, we demonstrate lead-free (K_xNa_1−x)NbO₃ single crystals with an ultrahigh large-signal piezoelectric coefficient d₃₃* of 9000 pm V⁻¹, which is superior to the highest value reported in state-of-the-art lead-based single crystals (~2500 pm V⁻¹). The enhanced electromechanical properties in our crystals are realized by an engineered compositional gradient in the as-grown crystal, allowing notable reversible non-180° domain wall motion. Moreover, our crystals exhibit temperature-insensitive strain performance within the temperature range of 25°C to 125°C. The enhanced temperature stability of the response also allows the materials to be used in a wider range of applications that exceed the temperature limits of current lead-based piezoelectric crystals.