Ultrahigh electrostrictive effect in potassium sodium niobate-based lead-free ceramics

The longitudinal electrostrictive coefficient Q₃₃ for perovskite-structured ferroelectric ceramics is usually between 0.01−0.04 m⁴/C². However, an ultra-low Q₃₃ of only 0.0047 m⁴/C² was identified in the 0.9K_0.5Na_0.5NbO₃-0.1SrTiO₃ (KNN-ST) composition. Despite the fact that superior piezoelectricity has been observed in KNN-based ceramics, this value is obviously much smaller than the normal value, according to the general cognition and the thermodynamic relationship between piezoelectric coefficient d₃₃ and Q₃₃. Therefore, we synthesized (1−x)(K_0.45Na_0.49Li_0.06)NbO₃-xSrTiO₃ (KNLN-ST) and studied phase structure, dielectric and ferroelectric properties systematically. Our findings show that the Q₃₃ in the KNLN-ST system (0.012−0.027 m⁴/C²) is within the reasonable range for perovskite-structured ferroelectric ceramics. Furthermore, an ultra-high electrostrictive strain (>0.3%) with ultra-low hysteresis was achieved in the 0.8KNLN-0.2ST sample. This research not only clarifies the electrostrictive effect in KNN-based systems, but it also broadens the potential application field of KNN-based ceramics to electrostrictive actuators.