Structure and electrical properties of Bi0.5(Na, K)0.5TiO3−BiGaO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x − y)Bi0.5Na0.5TiO3−xBi0.5K0.5TiO3− yBiGaO3 have been fabricated by an ordinary sintering technique, and their structure and electrical properties and depolarization temperature have been studied. The results of X-ray diffraction reveal that Bi0.5K0.5TiO3 and BiGaO3 diffuse into the Bi0.5Na0.5TiO3 lattices to form a new solid solution with a pure perovskite structure. An obvious change in microstructure with increasing concentration of Bi0.5K0.5TiO3 and BiGaO3 was observed. The piezoelectric constant d33 and the electromechanical coupling factor kp of the ceramics attain maximum values of 165 pC/N and 0.346 at y = 0.01(x = 0.18) and x = 0.21(y = 0.01), respectively. The temperature dependence of dielectric constant indicates an obvious relaxor characteristic with strong frequency dependence of dielectric constant. The depolarization temperature decreased with increasing content of BiGaO3 and first decreases and then increases with increasing amount of Bi0.5K0.5TiO3.