Insights into the correlation between strain and electrostrictive coefficient of potassium sodium niobate based ceramics from relaxor structure

Eco-friendly (K, Na)NbO₃ (KNN)-based electrostrictive materials have attracted increasing attention as potential candidates for high-precision displacement actuators. Although a series of breakthroughs have increased the electrostrictive coefficient of KNN-based materials with relaxor behaviour (Q₃₃ > 0.0450 m⁴/C²), the electrostrictive strain is still low (<0.1%), making the improvement of the electrostrictive strain a crucial next step. Here, a KNN-based relaxor ceramic of 0.96K_0.48Na_0.52Nb_1-xSb_xO₃-0.04Bi_0.5Na_0.5ZrO₃-0.3%Fe₂O₃ (KNNS_x-BNZ) was designed to simultaneously achieve high electrostrictive strain and Q₃₃. The phase structure transformed from the T phase to the C phase with increasing Sb concentration, which also introduced fine grains and domains. A high electrostrictive strain (～0.102%) and Q₃₃ (～0.0461 m⁴/C²) were obtained at x = 0.09 through a small adjustment of the structure of the relaxor, while an electrostrictive strain with low hysteresis (<10.5%) and an outstanding temperature stability (≥95%) were achieved in the broadened temperature range of 20–180 °C, representing properties superior to those of previous KNN-based and typical PZT-based materials. Our results will help researchers understand how to balance the strain and electrostrictive coefficient in lead-free materials, and thereby contribute toward accelerating the application of KNN-based electrostrictive materials in actuators.