Phase structures and electrical properties of K0.5Na0.5(Nb0.925Ta0.075)O3-LiSbO3 lead-free piezoelectric ceramics

Lead-free ceramics (1-x)K0.5Na0.5(Nb0.925Ta0.075)O3-xLiSbO3 have been prepared by an ordinary sintering technique. Our results reveal that Li+ and Sb5+ diffuse into the K0.5Na0.5(Nb0.925Ta0.075)O3 lattices to form a solid solution with a perovskite structure. The introduction of LiSbO3 into K0.5Na0.5(Nb0.925Ta0.075)O3 decreases 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 μC cm-2, coercive field Ec = 1.37 kV mm-1 and Curie temperature Tc = 354 deg. 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