Preparation And Piezoelectric Properties Of (Na_1/2Bi_1/2)TiO₃ Based Lead-free Ceramics

As one of the important functional ceramics, piezoelectric ceramics are widely used in mechanism, electrics and telecommunication. However, the widely used piezoelectric ceramics are mainly lead oxide-based perovsikte (eg: lead zirconate tiatanate), in which the content of lead oxide is more than 60%. The volatility of lead oxide pollutes the environment and does harm to people's healthiness. It is therefore very important to search an environmentally benign piezoelectric ceramics. As a consequence, much attention has been paid to lead-free piezoelectric ceramics in the past several years. In this thesis, (Bi_1/2Na_1/2)_0.94Ba_0.06TiO₃ ceramics with the compositions near the morphotropic phase boundary (MPB) were successfully prepared by soluble inorganic salt-chelate-gel method.The homogeneous, stable (Bi_1/2Na_1/2)_0.94Ba_0.06TiO₃ precursor were successfully prepared by ethylene glycol and acetic acid as solvent and citric acid as a chelate agent. The results show that the mole ratio of citric acid to total metal cation content r(CA) / r (Mⁿ⁺) is 1.5, and the PH value of precursor is 6～7.The analysis of TG, XPS, XRD and SEM demonstrats that the BNBT-6 ceramic powder annealed at 600℃for 2h is pure perovskite and contains the Bi, Na, Ti and Ba. The crystal grain of BNBT-6 ceramics prepared by soluble inorganic salt-chelate-gel method is equiaxial. The density of BNBT-6 ceramics tends to compact with the temperature increasing.The piezoelectric and dielectric properties of BNBT-6 were investigated. The piezoelectric constant (d₃₃) increases with sintering temperature, the maximum is 30×10^-12 C/No However, the relative dielectric constant increases firstly and decreases subsequently with sintering temperature, the minimum is 0.03。The microstructure, phase transition, piezoelectric and dielectric properties of multicomponent systems (0.94-x)(Bi_1/2Na_1/2)TiO₃-x(Bi_1/2K_1/2)TiO₃-0.06BaTiO₃ (BNT-BKT-BT) were studied. The results show that the rhombohedral-tetragona morphotropic phase boundary should lie in the composition of x=0.10, and the maximum piezoelectric of this composition is 41×10^-12 C / N.