Abstract: Lead free ferroelectric ceramics, (1-x)(0.97Na_0.5K_0.5NbO₃+0.03LiTaO₃)+xBiInO₃[(1-x)(KNN+LT)+xBI]  ternary solid solution system were prepared by conventional solid state reaction method. The polycrystal structure, dielectric and piezo-/ferro-electric properties were systematically characterized. The results show that the (1- x)(KNN+LT)+ xBI ceramics present pure perovskite structure in which the orthorhombic and tetragonal phases coexist at room temperature. With increasing of BI content, the tetragonal phase and the lattice parameter increase gradually and the Curie temperature Tc decreases, while the phase transition temperature To-t from orthorhombic to tetragonal phase increases. With more BI addition, the electric properties decrease with the appearance of oxygen vacancy due to Bi loss at high temperature. The optimal properties are achieved in the (1-x)(KNN+LT)+ xBI ceramics (x=0.0015) with the Curie temperature T_c= 400℃, phase transition temperature T_o-t =126℃, piezoelectric constant d₃₃ =160 pC/N, remnant polarization P_r=19.26 μC/cm² and coercive field E_c =7.75 kV/cm.

Key words: KNN-based ceramics, piezoelectric properties, phase transition, ferroelectric properties