Structure, piezoelectric and ferroelectric properties of Li- and Sb-modified K_0.5Na_0.5NbO₃lead-free ceramics

Lead-free ceramics (K0.5Na0.5)1-xLix(Nb1-ySby)O3have been prepared by an ordinary sintering technique. Li+and Sb5+diffuse into the K0.5Na0.5NbO3lattices to form a solid solution with the perovskite structure. The substitution of Li+increases the Curie temperature Tcand shifts the ferroelectric tetragonal-ferroelectric orthorhombic phase transition (TO-T) to low temperatures. On the other hand, the substitution of Sb5+decreases Tcand 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)O3ceramic, 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, SrCO3or Bi2O3leads to further enhancements of the piezoelectric and ferroelectric properties.