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

Abstract Plate-like NaNbO 3 (NN) particles were used as the raw material to fabricate (1 −  x )[0.93 K 0.48 Na 0.52 Nb O 3 –0.07Li(Ta 0.5 Nb 0.5 )O 3 ]– x NaNbO 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 K 3 Li 2 Nb 5 O 15 phase, and the tilting of the oxygen octahedron is probably responsible for the evolution of the tungsten–bronze-typed K 3 Li 2 Nb 5 O 15 phase. The Curie temperature ( T C ) is shifted to lower temperature with increasing NN content. (1 −  x )[0.93 K 0.48 Na 0.52 NbO 3 –0.07Li(Ta 0.5 Nb 0.5 )O 3 ]– x NaNbO 3 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 ( d 33 ) decrease with increasing amounts of NN. 0.01–0.03 mol of plate-like NaNbO 3 in 0.93 K 0.48 Na 0.52 NbO 3 –0.07Li(Ta 0.5 Nb 0.5 )O 3 gives the optimum content for preparing textured ceramics by the RTGG method.