Piezoelectric properties of K_0.47Na_0.47Li_0.06NbO₃-NaSbO₃lead-free ceramics for ultrasonic transducer applications

Lead-free piezoelectric ceramics (1-x)K0.47Na0.47Li0.06NbO3-xNaSbO3have been prepared by a conventional solid-state sintering technique. Our results reveal that NaSbO3diffuses into the K0.5Na0.5NbO3lattices to form a solid solution with a perovskite structure. After the addition of NaSbO3, both the paraelectric cubic-ferroelectric tetragonal and ferroelectric tetragonal-ferroelectric orthorhombic phase transition temperatures decrease. Coexistence of the orthorhombic and tetragonal phases is formed in the ceramics with x=0.04-0.10 at room temperature. In addition to the increase of the Na+/K+ratio and the strong covalence of Sb, the piezoelectricity of the ceramics is improved. For the ceramic with x=0.09, the piezoelectric properties become optimum, giving a piezoelectric coefficient d33of 305 pC/N, and electromechanical coupling factors kpand ktof 0.51. The ceramics also exhibit excellent performance in transducer applications, indicating that the ceramics are ready for replacing lead-containing ceramics in practical applications.