K/Na ratio-modulated design enables 1.32%-strain and 1383 pm/V-d33⁎ with high-temperature stability in sodium potassium niobate based ceramics

In recent years, there have been many significant breakthroughs in the research of potassium sodium niobate (KNN) based piezoelectric ceramics, positioning them as promising candidates for high-temperature piezoelectric device applications. To achieve synergistic optimization of high piezoelectric performance and high Curie temperature, the composition was designed to lie within the orthorhombic-tetragonal (O-T) phase coexistence region at room temperature by regulating the K/Na ratio, while the overall lattice stability was preserved. Our results show that the 0.96(KₓNa 1-x )(Nb 0.98 Sb 0.02 )O 3 -0.04Bi 0.5 Li 0.5 HfO 3 ceramic at x = 0.48 exhibits a high inverse piezoelectric constant of ~1383   pm/V and a strain of 1.32%, which are primarily attributed to the reduced polarization switching barrier enabled by the O-T phase coexistence at room temperature. Meanwhile, the local structural heterogeneity introduced by Sb 5+ and Hf 4+ doping further enhances the electrical strain response. Notably, the ceramic maintains a high Curie temperature of 276 °C, governed by the intrinsic lattice stability without significant compromise, confirming its great potential for high-temperature piezoelectric device applications.