Dielectric and Piezoelectric Properties of Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3-NaNbO3Lead-Free Ceramics

The ternary lead-free piezoelectric ceramics system of (1 − x) [0.88Na0.5Bi0.5TiO3-0.12K0.5Bi0.5TiO3] − xNaNbO3(x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) were synthesized by conventional solid state reaction method. The crystal structure, dielectric, piezoelectric properties and P-E hysteresis loops were investigated. The crystalline structure of all compositions is mono-perovskite phase ascertained by XRD, and the lattice constant was calculated from the XRD data. Temperature dependence of dielectric constant e r and dissipation factor tan δ measurement revealed that all compositions experienced two phase transitions: from ferroelectric to anti-ferroelectric and from anti-ferroelectric to paraelectric, and these two phase transitions have relaxor characteristics. Both transition temperatures Td and Tm are lowered due to introduction of NaNbO3. P-E hysteresis loops show that 0.88Na0.5Bi0.5TiO3-0.12K0.5Bi0.5TiO3 ceramics has the maximum Pr and E c corresponding to the maximum values of electromechanical coupling factor Kp and piezoelectric constant d33. The piezoelectric constant d33 and electromechanical coupling factor Kp decrease a little, while the dielectric constant e33 T /e0 improves much more when the concentration of NaNbO3 is 8 mol%.