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Abstract Lead-free piezoelectric composition ceramics of (1-x-y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yK0.5Na0.5NbO3; (1-x-y)BNT-xBKT-yKNN (with 0.18≤x ≤ 0.26 and 0≤y ≤ 0.07) were fabricated using the solid-state combustion method. The structure exhibited co-existing rhombohedral and tetragonal phases for all samples.… Click to show full abstract
Abstract Lead-free piezoelectric composition ceramics of (1-x-y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yK0.5Na0.5NbO3; (1-x-y)BNT-xBKT-yKNN (with 0.18≤x ≤ 0.26 and 0≤y ≤ 0.07) were fabricated using the solid-state combustion method. The structure exhibited co-existing rhombohedral and tetragonal phases for all samples. Increasing of x and y contents, the average grain size decreased from 1.42 μm to 1.02 μm and 1.25 μm to 0.70 μm, respectively. The diffuseness exponent (γ) of the ceramics was between 1.817 and 1.939 for x composition and between 1.766 and 1.999 for y composition indicating that the (1-x-y)BNT-xBKT-yKNN solid solutions had diffuse phase transition behavior. The change in the P-E loops of the ceramics indicated that the long-range ferroelectric order of the samples was disturbed and turned to the polar nano-regions (PNRs) with increased x and y contents. The polarization hysteresis loop transformed from well saturated typical ferroelectric, to pinched, and then to the relaxor state with increased x and y content. The addition of BKT and KNN contents significantly enhances the field-induced strain in BNT ceramics. The largest Smax of 0.25% corresponded to a high-field effective d33* of 509 pm/V, which was found in the composition of 0.79BNT-0.20BKT-0.01KNN.