Effects of substitution on electrical properties of (Bi1/2 Na1/2)TiO3-based lead-free ferroelectrics

Dielectric, ferroelectric and piezoelectric properties of bismuth sodium titanate, (Bi_1/2Na_1/2)TiO₃ (BNT) were studied on some additive dopants for a candidate as lead-free piezoelectric ceramics. Electromechanical coupling factors, k₃₃ in the longitudinal mode of BNT ceramics depend on the purity of starting raw materials and additive dopants. The k₃₃ for high and normal purities are 0.38 and 0.43, respectively. It is considered that impurities in starting materials are influence on piezoelectric properties. In the case of Mn addition, the Curie temperature, T_c , decreases rapidly with increasing amount of doped MnCO₃ , and the resistivity, ρ, is enhanced to 3×10¹⁴ (Ωcm) (at 40°C) for BNT+MnCO₃ 0.2 (wt.%). In the case of Nb addition, Nb⁵⁺ ions substitute for Ti⁴⁺ ions as a donor. The k₃₃ (=0.42) of Nb-doped BNT ceramics are larger than that of undoped BNT ceramic (=0.28) under the condition of the low poling field (E_p=5 kV/mm). In the case of Fe addition, Fe ³⁺ ions substitute for Ti⁴⁺ ions as a acceptor. The k₃₃ (=0.18) of Fe-doped BNT ceramics are smaller than that of undoped BNT ceramic (E_p=5 kV/mm)