Phase transition and piezoelectric properties of K0.48Na0.52NbO3–LiTa0.5Nb0.5O3–NaNbO3 lead-free ceramics

Plate-like NaNbO3 (NN) particles were used as the raw material to fabricate (1 − x)[0.93 K0.48Na0.52Nb O3–0.07Li(Ta0.5Nb0.5)O3]–xNaNbO3 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 K3Li2Nb5O15 phase, and the tilting of the oxygen octahedron is probably responsible for the evolution of the tungsten–bronze-typed K3Li2Nb5O15 phase. The Curie temperature (TC) is shifted to lower temperature with increasing NN content. (1 − x)[0.93 K0.48Na0.52NbO3–0.07Li(Ta0.5Nb0.5)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 (kp) and the piezoelectric constant (d33) decrease with increasing amounts of NN. 0.01–0.03 mol of plate-like NaNbO3 in 0.93 K0.48Na0.52NbO3–0.07Li(Ta0.5Nb0.5)O3 gives the optimum content for preparing textured ceramics by the RTGG method.

► The evolution of the crystal structure for the new phase K3Li2Nb5O15 was described.
► The dielectric relaxor behavior would be strengthened by increasing plate-like NN.
► kp and d33 decrease with increasing amount of plate-like NN.
► 0.01–0.03 mol of plate-like NN is a proper content for texturing ceramics by RTGG.