Structure, piezoelectric and ferroelectric properties of Li- and Sb-modified K0.5Na0.5NbO3 lead-free ceramics

Abstract

Lead-free ceramics (K0.5Na0.5)1−xLix(Nb1−ySby)O3 have been prepared by an ordinary sintering technique. Li+ and Sb5+ diffuse into the K0.5Na0.5NbO3 lattices to form a solid solution with the perovskite structure. The substitution of Li+ increases the Curie temperature Tc and shifts the ferroelectric tetragonal–ferroelectric orthorhombic phase transition (TO–T) to low temperatures. On the other hand, the substitution of Sb5+ decreases Tc and has a minor effect on TO–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 (K0.5Na0.5)0.94Li0.06(Na0.94Sb0.06)O3 ceramic, piezoelectric constant d33 = 212 pC N−1, planar and thickness electromechanical coupling factors kP = 46% and kt = 47% and Tc = 358 °C. The donor-type doping of BaCO3, SrCO3 or Bi2O3 leads to further enhancements of the piezoelectric and ferroelectric properties.