The fine-grained KNN–LN ceramics densified from nanoparticles obtained by an economical sol–gel route

Highlights: ► Fine-grained KNN–LN lead-free piezoelectric ceramics have been densified at the temperature below 1000 °C using sol–gel derived nano-particles as precursor oxides. ► The phase structure of the (1 − x)KNN–xLN ceramics changed from orthorhombic to tetragonal at x = 0.08–0.10, and the large improvements in the piezoelectric properties were observed for 0.90KNN–0.10LN. - Abstract: (1 − x)(K0.5Na0.5)NbO3–xLiNbO3 ((1 − x)KNN–xLN) nanoparticles with the mean particle size about 20–30 nm have been prepared by an economical sol–gel routes using Nb2O5 as Nb source. Due to the high sintering ability of nano-particles, fine-grained KNN–LN lead-free ceramics have been densified at the temperature below 1000 °C. X-ray diffraction analysis indicated that the phase structure of the ceramics changed from orthorhombic to tetragonal at x = 0.08–0.10. When the x reached 0.10 and above, the perovskite structure could not be maintained and the impurity phases of K3Li2Nb5O15 and LiNbO3 appeared, indicating that x = 0.10 is near the solubility limit. Optimized parameters, such as d33 = 170 pC/N and kp = 0.40, were achieved in 0.90KNN–0.10LN systems. Due to the merits of fine-grained structure and low sintering temperatures, it will be helpful to the application of KNN–LN materials for lead-free multilayer piezoelectric actuator.