Microstructure and electrical properties of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–LiNbO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics of (1−x−y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yLiNbO3 (BNT–BKT–LN-x/y) have been fabricated by a conventional solid-state reaction method, and their microstructure and electrical properties have been investigated. The results of X-ray diffraction (XRD) measurement show that K+, Li+ and Nb5+ diffuse into the Bi0.5Na0.5TiO3 lattices to form a solid solution with a pure perovskite structure. The BKT and LN addition has no remarkable effect on the crystal structure. However, a significant change in grain size took place. Simultaneously, with increasing amount of LN, the temperature for a ferroelectric–antiferroelectric phase transition is clearly reduced. The temperature dependence of dielectric properties suggests that the ceramics have diffuse-type phase transition characteristics. The piezoelectric constant d33 and the electromechanical coupling factor kp of the ceramics attain maximum values of 195 pC/N and 0.336 at x=0.18 and y=0.01.