The Effects of Ta Substitution and K/Na Ratio Variation on the Microstructure and Properties of (K,Na)NbO3-Based Lead Free Piezoelectric Ceramics

[(Na0.5+y K0.5−y )0.94Li0.06][(Nb0.94Sb0.06)1−x Ta x ]O3 + 0.08 mol% MnO2 lead-free piezoelectric ceramics were fabricated successfully by a conventional solid-state reaction method. The effects of Ta5+ substitution and K/Na ratio variation on the microstructure and properties of the ceramics have been systematically investigated. With the increasing of Ta5+ substitution content, the orthorhombic–tetragonal transition temperature T o–t presents obvious “V” type variation while the Curie temperature T c decreases monotonically. The ceramics properties were further enhanced by adjusting the Na/K ratio of the A-site. Under systematical optimization of the A-site and B-site elements, good overall electrical properties of d 33 = 276 pC/N, k p = 44.5%, e 33 T /e 0 = 1,175, tanδ = 0.027, T c = 309 °C, P r = 21.0 μC/cm2, and E c = 1.14 kV/mm were obtained for ceramics with Ta5+ content x of 0.05 and Na/K ratio of 57/43 (y = 0.07).