Structure and electrical properties of K_0.5Na_0.5NbO₃-LiSbO₃lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1-x)K0.5Na0.5NbO3-xLiSbO3have been fabricated by a conventional ceramic sintering technique. The results of x-ray diffraction suggest that Li+and Sb5+diffuse into the K0.5Na0.5NbO3lattices to form a solid solution with a perovskite structure. The ceramics can be well sintered at 1070-1110°C. The introduction of LiSbO3into the Na0.5K0.5NbO3solid solution decreases slightly the paraelectric cubic-ferroelectric tetragonal phase transition temperature (Tc), but greatly shifts the ferroelectric tetragonal-ferroelectric orthorhombic phase transition (TO-F) to room temperature. Coexistence of the orthorhombic and tetragonal phases is formed at 0.05 <x< 0.07 at room temperature, leading to a significant enhancement of the piezoelectric properties. For the ceramic with x=0.06, the piezoelectric properties become optimum: piezoelectric constant d33=212 pC/N, planar and thickness electromechanical coupling factors kp=46% and kt=41%, respectively, remanent polarization Pr=15.0 μC/cm2, coercive field Ec= 1.74 kV/mm, and Curie temperature TC=358°C.