Improved piezoelectric properties of (KxNa1−x)0.94Li0.06NbO3 lead-free ceramics fabricated by combining two-step sintering

The effects of K/Na ratio on the phase structure, microstructure and electrical properties of (KxNa1−x)0.94Li0.06NbO3 (KxNLN, x = 0.34–0.61) lead-free piezoelectric ceramics were studied. Results showed that samples with x = 0.46–0.52 have a coexisted crystal structure with both orthorhombic and tetragonal phases, separating orthorhombic phase on both sides of this composition and corresponding to a polymorphic phase transition near room temperature. In this region, enhanced electrical properties were obtained. The approach of two-step sintering obviously broadened the sintering temperature range of the ceramics and further improved piezoelectric properties by ∼10%, indicating it is a promising way for fabricating (K, Na)NbO3-based ceramics. Moreover, all studied samples showed good resistance to thermal depoling up to temperatures close to their Curie points, suggesting that this system should be an attractive lead-free material for piezoelectric applications.

► This work presents interesting results on structure property relation of KxNLN-based ceramics.
► A coexisted structure and enhanced electrical properties were obtained in KxNLN-based ceramics.
► Two-step sintering broadened the sintering temperature range and further improved performance.
► All studied samples showed good resistance to thermal depoling up to ∼450 °C.