Ultra-Stable Thermal Piezoelectricity up to 200 °C in High-Performance KNN-Based Textured Piezoceramics

The challenge of simultaneously achieving optimal piezoelectric properties and thermal stability in lead-free ceramics serves as a limiting factor on their potential applications. To overcome this predicament, a dual strategy integrating composition modulation and texture engineering is proposed with the purpose of restructuring the complex coupling between the phase structure, domain configuration, crystal anisotropy, and phase transition of (K,Na)NbO₃-based ceramics. As a result, a high piezoelectric coefficient (d₃₃ ∼ 550 ± 30 pC N⁻¹), and an inverse piezoelectric coefficient (d₃₃^* ∼ 850 pm V⁻¹), as well as a Curie temperature T_C of 290 °C, are obtained in (K,Na)NbO₃-based textured ceramics. Most importantly, in the temperature range of 25–200 °C, the maximum permitted fluctuations of d₃₃ and d₃₃^* of the (K,Na)NbO₃-based ceramics are only 3% and 4%, respectively. This ultra-stable thermal piezoelectricity displayed in (K,Na)NbO₃-based ceramics is comparable to that of commercial Pb(Zr,Ti)O₃-based ceramics. This work not only enhances the potential of (K,Na)NbO₃-based ceramics to replace Pb(Zr,Ti)O₃-based ceramics in high-temperature service, but also offers critical insights into the rational design of lead-free piezoelectric ceramics for broad-temperature-range applications.