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 εr 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 Ec 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 ε33T/ε0 improves much more when the concentration of NaNbO3 is 8 mol%.