Dielectric and piezoelectric properties of Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3-NaNbO3 lead-free ceramics

The ternary lead-free piezoelectric ceramics system of (1 - x) [0.88Na(0.5)Bi(0.5)TiO(3)-0.12K(0.5)Bi(0.5)TiO(3)] - xNaNbO(3)(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 epsilon(r) and dissipation factor tan delta 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 T-d and T-m are lowered due to introduction of NaNbO3. P-E hysteresis loops show that 0.88Na(0.5)Bi(0.5)TiO(3)-0.12K(0.5)Bi(0.5)TiO(3) ceramics has the maximum P-r and E-c corresponding to the maximum values of electromechanical coupling factor K-p and piezoelectric constant d(33) The piezoelectric constant d33 and electromechanical coupling factor K-p decrease a little, while the dielectric constant epsilon(T)(33)/epsilon(0) improves much more when the concentration of NaNbO3 is 8 mol%.