Structure and piezoelectric properties of K0.5Na0.5NbO3 based lead-free piezoceramics with slight deviation from A-site K or Na stoichiometry

Abstract

The dependence of structure and piezoelectric response d33 on individual excess A-site K or Na in K0.5Na0.5NbO3 based lead-free piezoceramics is reported. The coexistence of orthorhombic, tetragonal, and monoclinic phases at room temperature is observed in the investigated 0.94K0.5+xNa0.5NbO3–0.06LiNbO3 and 0.94K0.5Na0.5+yNbO3–0.06LiNbO3 ceramics (x, y = 0–0.025). The weight ratio of three phases, orthorhombic-tetragonal phase transition temperature, and d33 value are highly sensitive to A-site K or Na nonstoichiometry. A-site Na nonstiochiometry plays a dominant role in enhancing the electrical properties of KNN by significantly reducing the weight ratio percentage of monoclinic phase and shifting the orthorhombic-tetragonal phase transition temperature to lower temperatures.