High Electrostrain with Low Hysteresis Realized in Pb-Free Perovskite via Defect Engineering

High-precision applications in electromechanical actuation heavily rely on piezoelectric materials that exhibit high electrostrain output with low hysteresis. Here, we report a large electrostrain of 1.53% together with low hysteresis of 12.5%, being achieved by incorporating a nominal oxygen-deficient modifier, SmZnO_2.5, into a Bi_1/2(Na_0.5K_0.5)_1/2TiO₃ matrix. The excellent stability of the skin-like layered structure enables the strain to be maintained over a wide temperature range, spanning from room temperature to 200 °C. The giant strain stems from two main factors, i.e., the defect dipoles with stronger polarization along the [001] direction align with the electric field, thereby enhancing the polarization rotation, as well as the electrobending effect synergistically contributing to these results. Note that strongly polar defect dipoles and dislocations are the key to bending behavior. Importantly, the presence of defect dipoles and dislocations destroys the long-range ferroelectric order, forming 2-5 nm polar nanoregions that induce the observed slim hysteresis behavior. Our research uncovers the potential application of BNT-based materials in actuators with large output displacement and provides a universally applicable methodology to realize large strain with low hysteresis.