Properties of Co-doped 0.92(Na_0.5Bi_0.5) TiO₃-0.08BaTiO₃lead-free ceramics

Lead-free piezoelectric ceramics 0.92(Bi0.5Na0.5)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 Qmsignificantly, 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 kp. The present 0.92(Bi0.5Na0.5)TiO3-0.08BaTiO3+3.5mol% Co3+ceramics exhibit good performance with mechanical quality factor Qm= 910, piezoelectric constant d33= 106pC/N, planar electromechanical coupling kp= 10% and dissipation factor tan δ = 1.1% at 1kHz. Saturated polarization hysteresis loops have been obtained for BNBT-Co ceramics. Two dielectric peaks at depolarization temperature Tdand Tmappear in the curves ofT33vs temperature for the pure BNBT ceramics. However, the first dielectric peak Tddisappears after the addition of Co3+, which means that the transition from ferroelectric to antiferroelectric phase has been eliminated.