Phase structures and electrical properties of K_0.5Na_0.5(Nb_0.925Ta_0.075)O₃-LiSbO₃lead-free piezoelectric ceramics

Lead-free ceramics (1-x)K0.5Na0.5(Nb0.925Ta0.075)O3-xLiSbO3have been prepared by an ordinary sintering technique. Our results reveal that Li+and Sb5+diffuse into the K0.5Na0.5(Nb0.925Ta0.075)O3lattices to form a solid solution with a perovskite structure. The introduction of LiSbO3into K0.5Na0.5(Nb0.925Ta0.075)O3decreases the Curie temperature (Tc) slightly, but shifts the ferroelectric tetragonal-ferroelectric orthorhombic phase transition temperature (TO-T) significantly to low temperatures. As a result, the ceramics have an orthorhombic phase at x ≤ 0.02 and tetragonal phase at x ≥ 0.04. Coexistence of the orthorhombic and tetragonal phases is formed at 0.02 < x < 0.04 near room temperature, leading to significant enhancements of the piezoelectric properties. For the ceramic with x ≤ 0.035, the piezoelectric properties become optimum giving: piezoelectric coefficient d33≤ 244 pC N-1, electromechanical coupling factors kP≤ 51% and kt≤ 46%, remanent polarization Pr≤ 20.1 νC cm-2, coercive field Ec≤ 1.37 kV mm-1and Curie temperature Tc≤ 354 °C. The ceramic has good temporal and thermal stability, greatly improved electrical properties and a relatively high Curie temperature, suggesting that it is a promising lead-free replacement for lead-based piezoelectric ceramics.