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 0.96K0.48Na0.52Nb1-xSbxO3-0.04Bi0.5Na0.5ZrO3-0.3%Fe2O3 (KNNSx-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.