Microstructure and piezoelectric properties of (1-x)(Na_0.5K _0.5)NbO_3-xLiNbO₃ ceramics

(1-x)(Na0.5K0.5)NbO3-xLiNbO3 [(1-x)NKN-xLN] ceramics were produced by the conventional solid-state sintering method, and their microstructure and piezoelectric properties were investigated. The formation of the liquid phase and K6Li4Nb10O30 second phase that were observed in the (1-x)NKN-xLN ceramics was explained by the evaporation of Na2O during the sintering. A morphotropic phase boundary (MPB) was observed in the specimens with 0.05<x<0.08. Promising piezoelectric properties were obtained for the specimens with x=0.07. Therefore, the piezoelectric properties of this 0.93NKN-0.07LN ceramic were further investigated and were found to be influenced by their relative density and grain size. In particular, grain size considerably affected the d33 value. Two-step sintering was conducted at different temperatures to increase the grain size. Piezoelectric properties of d33=240 (pC/N) and kp=0.35 were obtained for the 0.93NKN-0.07LN ceramics sintered at 1030°C and subsequently annealed at 1050°C.