Boosting piezoelectric response in lead-free KNN crystals via direct current and alternating current poling

Ferroelectric materials with strong piezoelectric responses are critical for high-performance electromechanical devices. Alternating current poling (ACP) has been shown to effectively enhance the piezoelectric and electromechanical properties of PbTiO₃-based relaxor crystals. In this study, we introduce a combined direct current poling (DCP) and ACP strategy to improve the properties of K_0.62Na_0.38NbO₃ single crystals. The DCP + ACP method promotes polarization rotation, resulting in a net macroscopic polarization that exceeds that of crystals processed by conventional DCP alone. Domain characterization reveals that this approach produces a refined domain configuration in which 120° and 60° domains coexist. A peak piezoelectric coefficient (d₃₃) of 330 pC/N is achieved, with a maximum performance improvement of 71.9% over standard DCP. These findings demonstrate a viable route for enhancing piezoelectric performance in lead-free materials through domain engineering.