Dielectric, piezoelectric, and ferroelectric properties of MnCO3-added 74(Bi1/2Na}1/2) TiO3-20.8(Bi1/2K1/2)TiO3-5.2BaTiO3 lead-free piezoelectric ceramics

74(Bi_1/2Na_1/2)TiO{i3}-20.8(Bi_1/2K_1/2)TiO₃-5.2BaTiO₃-x MnCO₃ lead-free piezoelectric ceramics were synthesized by conventional solid oxide routine. The tetragonal 74(Bi_1/2Na_1/2)TiO₃-20.8(Bi_1/2K_1/2)TiO₃-5.2 BaTiO₃ (BNKB) exhibits high depolarization temperature T_d of 195??C; however, its properties are far from satisfactory for practical application and need to be improved. The experiments show that the addition of MnCO₃ reduces the tetragonality c/a and increases the cell volume. In addition, it revealed that the suitable addition of MnCO₃ promotes the sintering and increases the densities of BNKB ceramics. The addition of MnCO₃ also enhances the relaxor behavior of BNKB ceramics due to the reconstruct of the disorder arrays. Due to the effect of the crystal lattice, grain growth, and relaxor behavior, the optimal electric properties were realized at MnCO₃ addition x of 0.16: the dielectric permittivity ??_r = 1047, dielectric dissipation tan?? = 0.022, piezoelectric strain d₃₃ = 140 pC/N, mechanical coupling k_p = 0.18, mechanical quality Q_m = 89 while the depolarization temperature T_d stays relatively high at 175??C. The effect and mechanism of Mn doping on the electrical properties were discussed in detail.