Phase transition and piezoelectric properties of K_0.48Na _0.52NbO₃-LiTa_0.5Nb_0.5O ₃-NaNbO₃ lead-free ceramics

Plate-like NaNbO₃ (NN) particles were used as the raw material to fabricate (1 - x)[0.93 K_0.48Na_0.52Nb O ₃-0.07Li(Ta_0.5Nb_0.5)O₃]-xNaNbO ₃ lead-free piezoelectric ceramics using a conventional ceramic process. The effects of NN on the crystal structure and piezoelectric properties of the ceramics were investigated. The results of X-ray diffraction suggest that the perovskite phase coexists with the K₃Li₂Nb ₅O₁₅ phase, and the tilting of the oxygen octahedron is probably responsible for the evolution of the tungsten-bronze-typed K ₃Li₂Nb₅O₁₅ phase. The Curie temperature (T_C) is shifted to lower temperature with increasing NN content. (1 - x)[0.93 K_0.48Na_0.52NbO₃-0. 07Li(Ta_0.5Nb_0.5)O₃]-xNaNbO₃ ceramics show obvious dielectric relaxor characteristics for x > 0.03, and the relaxor behavior of ceramics is strengthened by increasing NN content. Both the electromechanical coupling factor (k_p) and the piezoelectric constant (d₃₃) decrease with increasing amounts of NN. 0.01-0.03 mol of plate-like NaNbO₃ in 0.93 K_0.48Na_0.52NbO ₃-0.07Li(Ta_0.5Nb_0.5)O₃ gives the optimum content for preparing textured ceramics by the RTGG method.