Piezoelectric and ferroelectric properties of Li-doped (Bi _0.5Na_0.5)TiO₃-(Bi_0.5K _0.5)TiO₃-BaTiO₃ lead-free piezoelectric ceramics

The piezoelectric and ferroelectric properties of 0.852[Bi _0.5(Na_(1-x)Li_x)_0.5]TiO ₃-0.110(Bi_0.5K_0.5)TiO₃-0. 038BaTiO₃ (x=0, 0.02, 0.05, 0.10, 0.15, and 0.30, abbreviated as BNKLBTx) lead-free piezoelectric ceramics were prepared by conventional ceramic processing. X-ray diffraction on the samples revealed that Li⁺ ions diffused into the Bi_0.5Na_0.5TiO₃ lattices (A-site) and formed a solid solution with a single perovskite structure. All the samples could be sintered at 1160°-1180°C, with the density being on the order of >95% of the theoretical. The ceramics with x=0.10 exhibited the highest properties, with the piezoelectric coefficient being on the order of d₃₃=235 pC/N, while the electromechanical coupling factors were found to be k_p=0.30 and k_t=0.45, respectively. The dielectric, pyroelectric, electromechanical, and ferroelectric behaviors were investigated as a function of temperature. It was found that the depolarization temperature T_d showed a strong dependence on the content of Li⁺ addition, shifting to a lower temperature with increasing Li⁺ dopant.