Piezoelectric Properties of K _0.47 Na _0.47 Li _0.06 NbO ₃ –NaSbO ₃ Lead‐Free Ceramics for Ultrasonic Transducer Applications

Lead‐free piezoelectric ceramics (1− x )K _0.47 Na _0.47 Li _0.06 NbO ₃ – x NaSbO ₃ have been prepared by a conventional solid‐state sintering technique. Our results reveal that NaSbO ₃ diffuses into the K _0.5 Na _0.5 NbO ₃ lattices to form a solid solution with a perovskite structure. After the addition of NaSbO ₃ , 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 d ₃₃ of 305 pC/N, and electromechanical coupling factors k _p and k _t of 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.