Phase transition behavior and electrical properties of [(K0.50Na0.50)1−xAgx](Nb1−xTax)O3 lead-free ceramics

The effect of AgTaO3 on the electrical properties of (K0.5Na0.5)NbO3 lead-free ceramics was systematically investigated, and the phase transition behavior of the ceramics was also studied in terms of high temperature X-ray diffraction. The experimental results show that Ag+ and Ta5+ ions diffuse into the (K0.5Na0.5)NbO3 lattices to form a stable solid solution with orthorhombic structure, and also lead to the decrease in the orthorhombic to the tetragonal phase transition temperature and the Curie temperature. The 0.92(K0.5Na0.5)NbO3-0.08AgTaO3 ceramics exhibit optimum electrical properties (d33 = 183 pC/N, kp = 41%, Tc = 356 °C, To-t = 158 °C, ɛr ∼ 683, and tan δ ∼ 3.3%) and good thermal-depoling behavior. The piezoelectric properties of (1 − x)(K0.5Na0.5)NbO3-xAgTaO3 ceramics are much superior to pure (K0.5Na0.5)NbO3 ceramics. X-ray diffraction patterns for the 0.92(K0.5Na0.5)NbO3-0.08AgTaO3 ceramic at different temperatures indicated a pure perovskite phase with an orthorhombic structure at below 160 °C, a tetragonal structure at 160-350 °C, and a cubic structure at above 360 °C. As a result, the (1 − x)(K0.5Na0.5)NbO3-xAgTaO3 ceramic is one of the promising candidate materials for lead-free piezoelectric ceramics.