Phase transition behavior and electrical properties of [(K 0.50Na 0.50) 1− xAg x](Nb 1− xTa x)O 3 lead-free ceramics

Abstract

The effect of AgTaO 3 on the electrical properties of (K 0.5Na 0.5)NbO 3 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 Ta 5+ ions diffuse into the (K 0.5Na 0.5)NbO 3 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(K 0.5Na 0.5)NbO 3–0.08AgTaO 3 ceramics exhibit optimum electrical properties ( d 33 = 183 pC/N, k p = 41%, T c = 356 °C, T o–t = 158 °C, ɛ r ∼ 683, and tan δ ∼ 3.3%) and good thermal-depoling behavior. The piezoelectric properties of (1 − x)(K 0.5Na 0.5)NbO 3– xAgTaO 3 ceramics are much superior to pure (K 0.5Na 0.5)NbO 3 ceramics. X-ray diffraction patterns for the 0.92(K 0.5Na 0.5)NbO 3–0.08AgTaO 3 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)(K 0.5Na 0.5)NbO 3– xAgTaO 3 ceramic is one of the promising candidate materials for lead-free piezoelectric ceramics.