Structure evolution and exceptionally ultra-low hysteresis unipolar electric field-induced strain in (1−x)NaNbO₃-xBaTiO₃ lead-free ferroelectrics

In actuators, large-signal electric field-induced strains with low hysteresis are required for practical applications, since large hysteresis would seriously affect the design and performance of the actuators. Here we report on ultra-low hysteresis electric field-induced strain in lead-free (1−x)NaNbO₃-xBaTiO₃ (NN-BT) ferroelectrics. With respect to the increasing of the BT content from 0.10 to 0.27, a tetragonal-to-cubic transition is identified at x = 0.22 by x-ray diffraction structural refinement. This phase transition is also supported by the temperature-dependent dielectric properties. Unipolar large-signal strains (at 40 kV/cm) with very low hysteresis (< 10%) are observed for x = 0.10–0.22. In addition, for x = 0.10, almost linear strain with a temperature variation less than 10% is observed from 30 °C to 120 °C. This study suggests that the NN-xBT system and related NN-based materials can be considered as potential materials used in high-precision actuators, and also evoke the interest to study the origin of such ultra-low hysteresis electric field-induced strains in the fundamental research aspect.