Properties of Co-Doped 0.92(Na_0.5Bi_0.5) TiO₃-0.08BaTiO₃ Lead-Free Ceramics

Lead-free piezoelectric ceramics 0.92(Bi_0.5Na_0.5)TiO₃-0.08BaTiO₃+xmol% Co³⁺ (BNBT-Co, x=0--8) are prepared by the solid state reaction method. Effects of the amount of Co³⁺ on the electrical properties and phase transition are studied. The results indicate that the addition of Co³⁺ enhances the mechanical quality factor Q_m significantly, whereas the dissipation factor tan δ has a minimum value at x=3.5. Meanwhile, addition of Co³⁺ leads to small decreases of piezoelectric constant d₃₃, and planar electromechanical coupling k_p. The present 0.92(Bi_0.5Na_0.5)TiO₃-0.08BaTiO₃+3.5mol% Co³⁺ ceramics exhibit good performance with mechanical quality factor Q_m=910, piezoelectric constant d₃₃=106pC/N, planar electromechanical coupling k_p=10% and dissipation factor tanδ=1.1% at 1kHz. Saturated polarization hysteresis loops have been obtained for BNBT-Co ceramics. Two dielectric peaks at depolarization temperature T_d and T_m appear in the curves of ε^T₃₃ vs temperature for the pure BNBT ceramics. However, the first dielectric peak T_d disappears after the addition of Co³⁺ which means that the transition from ferroelectric to antiferroelectric phase has been eliminated.