Broad Temperature Plateau for High Piezoelectric Coefficient by Embedding PNRs in Singe‐Phase KNN‐Based Ceramics

Abstract To date, the enormous potential of lead‐free piezoceramics in ultrasonic transducers and micro‐actuators has driven extensive research and development. Although the piezoelectric coefficient (d₃₃) of lead‐free ceramics is improved unprecedentedly, the breakthrough in comprehensive performance is still a key issue, one of which is the inverse relationship between d₃₃ and Curie temperature (T_C), and the other is the temperature stability of piezoelectricity. Here, based on the synergistic optimization of the chemical component modulation and texture technology, the high Curie temperature (≈365 °C), high piezoelectric properties (d₃₃ ≈331 pC/N, d₃₃^* ≈561 pm V⁻¹) and advanced piezoelectric temperature stability are realized by embedded PNRs in the conceived and prepared lead‐free single phase 0.96((K_0.5Na_0.5)(Nb_0.98Ta_0.02)O₃)‐0.01(Bi(Ni_0.67Nb_0.33)O₃)‐0.03(Bi_0.5K_0.5)HfO₃ texture ceramics. The d₃₃ changes by only 2.0% when the temperature is increased from 25 to 100 °C (≈10.0% to 200 °C), while the electrical strain (d₃₃^*) changes by only 4.2% when the temperature is increased from 25 to 175 °C (≈9.8% to 200 °C), which is comparable to the commercial lead‐based materials (i.e., PZT‐4). This work demonstrates significant progress in the comprehensive piezoelectric performance (especially the piezoelectric temperature stability) of lead‐free ceramics and inspires further attempts to achieve high‐temperature piezoelectric properties.