Structure and electrical properties' investigation of (K _0.5Na_0.5)NbO₃-(Bi_0.5Na _0.5)TiO₃ lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 - x)(K_0.5Na _0.5)NbO₃-x(Bi_0.5Na_0.5)TiO ₃ [(1 - x)KNN-xBNT] were synthesized by conventional solid-state sintering. The phase structure and electrical properties of (1 - x)KNN-xBNT ceramics are investigated. The polymorphic phase transition (from the orthorhombic to the tetragonal phase) (PPT) plays a very important role in (1 -x)KNN-xBNT ceramics. A PPT at room temperature in (1 - x)KNN-xBNT ceramics is identified for 0.02 < x ≤ 0.03. The (1 - x)KNN-xBNT (x = 0.025) ceramics show optimum electrical properties (d₃₃ ≃ 256 pC N^-1, d₃₁ = 85 pC N^-1, k_p = 0.48, k_t = 0.52 and T_C = 373 °C). The related mechanisms for high piezoelectric properties in (1 - x)KNN-xBNT (x = 0.025) ceramics are also discussed. These results indicate that the (1 - x)KNN-xBNT (x = 0.025) ceramic is a promising lead-free piezoelectric candidate material.