Effects of AC- and DC-bias field poling on piezoelectric properties of Bi-based ceramics

抄録

The structural and electrical properties of 0.75BiFeO₃–0.25BaTiO₃ (BF25BT) ceramics, with and without heat treatment, were investigated. The polished and cut BF25BT ceramics were thermally annealed at 800°C for 20 h and then quenched in water at room temperature (heat-treated ceramics). The P–E hysteresis loop and S–E curve were significantly improved after the heat treatment process. Meanwhile, the leakage current density at an electric field of 50 kV/cm was reduced from 4.847 × 10⁻⁷ (as-sintered ceramics) to 3.213 × 10⁻⁸ A/cm² (heat-treated ceramics). The heat-treated ceramics was poled at 120°C with applying a DC-bias field of 50 kV/cm, and the maximum phase angle was −39°, which was evaluated from the analysis of frequency-dependence of impedance and phase angle. Because of the small maximum phase angle obtained by poling under DC-bias field alone, the poling process was modified; that is, an AC-bias field was applied prior to the DC-bias field poling. The ceramics poled with the modified poling procedure exhibited the maximum phase angle of 63°. The appreciable increase of the maximum phase angle suggested the higher degree of domain alignment than that of its counterpart, and the effect was explained in terms of improved domain switching. The piezoelectric constant d₃₃ was increased twice with adopting the modified poling process, which signifies that poling with both AC- and DC-bias field is highly effective in the lead-free Bi-based systems.