Simultaneously achieving superior piezoelectric properties and good piezoelectric thermal stabilities in <001>-textured (K,Na)NbO3-based ceramic

(K,Na)NbO₃-based ceramics are widely regarded as a promising type of lead-free piezoelectric materials to replace the current lead-containing ones. However, due to polymorphic phase transitions, achieving a desirable comprehensive piezoelectric performance of high piezoelectric coefficient d ₃₃ and large electromechanical coupling factors k p , k t and k 33 along with good thermal stabilities (which are characterized by minimal temperature dependence and ageing degradation) in them is extremely challenging. The poled and subsequently thermally-stabilized <001>-textured 0.98(K₀.₄₈Na₀.₅₂)₀.₉₉Li₀.₀₁(Nb₀.₉₈Sb₀.₀₂)O₃–0.02(Bi₀.₅₀Na₀.₅₀)ZrO₃ ceramic was recently identified as an effective solution to the issue. It possesses a d ₃₃ of 405 pC/N along with k ₚ ≈ 0.80, k ₜ ≈ 0.60, k ₃₃ ≈ 0.88 at room temperature, and its piezoelectric properties are of weak temperature dependence across a broad operational range and show remarkable retention even after thermal ageing at 250 °C. Particularly, its d ₃₃ has an average of 425 pC/N with the variation ≤ ± 6.5% from room temperature to 100 °C, and its k ₜ keeps almost constant between -60 °C and 110 °C. In general, this ceramic exhibits an outstanding comprehensive performance that well competes to those of benchmark commercial piezoceramics such as PZT-5A and PZT-5H, indicating the great potential for advanced ultrasonic applications. Analysis reveals that the excellent piezoelectric properties originate from the synergistic effect of crystallographic anisotropy and an engineered, dense domain structure of orthorhombic phase. Meanwhile, the remarkable thermal ageing stability is possibly attributed to the relaxed crystal structure and the stabilized domain structure, both facilitated by the repeated orthorhombic-tetragonal phase transitions in the thermal treatment.