Modified Re-Entrant-Like (K, Na)NbO₃-Based Relaxors with Superior Electrostrain Properties

Piezoceramics with large strain output, low hysteresis, and wide operation temperature are indispensable for the high-end displacement control. Unfortunately, requiring these merits simultaneously remains a long-standing challenge for lead-free piezoceramics promising for replacing lead-based ones. Herein a new strategy to resolve this challenge by developing modified re-entrant-like potassium sodium niobate ((K, Na)NbO₃, KNN) relaxors is presented. Multi-scale structural analysis reveals the presence of the significant local disorder, nano-sized multi-phase coexistence, and ultra-fine grains, which facilitate the polarization rotation, effectively eliminate non-180° domains, and erase polymorphic phase transition features in re-entrant-like KNN relaxors. Consequently, a combination of large strain (≈0.19%), ultra-low hysteresis (<7%), high electrostriction coefficient (Q₃₃ = 0.049 m⁴ C⁻²), and benign temperature stability (i.e., strain varies less than 10.6% within 30–120 °C) is realized, superior to other lead-free relaxors. Therefore, this strategy provides a novel paradigm for designing high-performance lead-free piezoceramics used for high-precision actuators.