Research And Development Of Bi_0.5Na_0.5 TiO₃-Based Lead-free Piezoelectric Ceramics

Lead-free piezoelectric ceramic (1-x)Bi0.5Na0.5TiO3-xBaTiO3 (BNBT,BNBTx) has attracted much interest due to the superior piezoelectric performance with the x in the rhombohedral region near morphotropic phase boundary (MPB). Nevertheless, compared to the traditional piezoelectric ceramics Pb(Zr1–xTix)O3 (PZT), the piezoelectric and electromechanical response is still lower. In order to further improve it, in present work the BNBT ceramics was modified through designing ternary solid solution along with ionic doping. The main works in this dissertation are as follows:1. Based on BNBT with x of 0.065 (MPB composition), the effect of Mn addition on the dielectric, piezoelectric, and ferroelectric properties was studied. Results indicated that the Mn doping led to a substantial decrease in the dielectric loss along with an improvement in the piezoelectric constant and electromechanical coupling coefficient.2. Through substitution of Li+ into Na+ in BNBMT0.065 ceramic, the ternary-component lead-free piezoelectric ceramic of (0.935-x)Bi0.5Na0.5TiO3-0.065BaTiO3-xLi0.5Bi0.5TiO3-0.5%Mn was prepared and studied. The Li+ substitution could improve the sintering characteristics and decreased the sintering temperature. Besides, at a critical composition of x=0.06, the optimal global properties of d33 of 172 pC/N, kp of 33%, of 837 and tanδof 0.026 were obtained.3. The effect of Nb, Fe, Ce, and La doping on the dielectric, piezoelectric, and ferroelectric properties in BNLBMT0.06 ceramics was studied. The optimal electric properties were obtained for the La-doped ceramics. The piezoelectric constant, electromechanical coupling coefficient could reach 184 pC/N and 0.32, respectively.4. (1−x)(0.935Bi0.5Na0.5TiO3–0.065BaTiO3)–xKNbO3 ceramics with x ranging from 0 to 0.1 were prepared. A large electrostrictive coefficient of ~10-2 m4C-2 is obtained with the composition x ranging from 0.02 to 0.1, which is even higher than the well-known electrostrictive material Pb(Mg1/3Nb2/3)O3. Under an electric field of 4 kV/mm, the electrostrictive strain can reach as high as 0.08%. Besides, the electric field induced strain behavior indicates a temperature independent behavior within the temperature range of 20 to 150 oC. The large electrostrictive strain is suggested to be ascribed to the formation of non-polar phase developed by the KNbO3 substitution and the high electrostrictive coefficient of the designed ceramics make them great potential to be applied to the new solid-state actuators.