Structure, piezoelectric and ferroelectric properties of Li- and Sb-modified K0.5Na0.5NbO3lead-free ceramics

Lead-free ceramics (K 0.5 Na 0.5 ) 1− x Li x (Nb 1− y Sb y )O 3 have been prepared by an ordinary sintering technique. Li + and Sb 5+ diffuse into the K 0.5 Na 0.5 NbO 3 lattices to form a solid solution with the perovskite structure. The substitution of Li + increases the Curie temperature T c and shifts the ferroelectric tetragonal–ferroelectric orthorhombic phase transition ( T O–T ) to low temperatures. On the other hand, the substitution of Sb 5+ decreases T c and has a minor effect on T O–T . The coexistence of the orthorhombic and tetragonal phases at x = 0.06 and y = 0.06 near room temperature and the strong covalence of Sb lead to significant improvements in the piezoelectric properties. For the (K 0.5 Na 0.5 ) 0.94 Li 0.06 (Na 0.94 Sb 0.06 )O 3 ceramic, piezoelectric constant d 33 = 212 pC N −1 , planar and thickness electromechanical coupling factors k P = 46% and k t = 47% and T c = 358 °C. The donor-type doping of BaCO 3 , SrCO 3 or Bi 2 O 3 leads to further enhancements of the piezoelectric and ferroelectric properties.