| Sodium bismuth titanate ((Na0.5Bi0.5)TiO3, abbreviated as NBT) is a kind of pervoskite ferroelectric with complex A-site cations, showing a relatively large remanent polarization (Pr=38 μC/cm2) at room temperature and a relatively high Curie temperature (T=320℃). Due to its strong ferroelectricity, NBT-based ceramics are considered to be one group of promising lead-free piezoelectric ceramics. In this thesis, 0.94 (Nao.5Bio.5)TiO3-0.06BaTiO3-xwt%CeO2 (abbreviated as NBT-BT6-x%CeO2) superfine powders were synthesized by a citrate method. The synthesis process, piezoelectric and ferroelectric properties of NBT-BT6-x%CeO2 ceramic specimens were investigated. The influence of poling process on the piezoelectric properties of NBT-BT6-x%CeO2 ceramic specimens was investigated. The effect of sintering temperature on the piezoelectric and ferroelectric properties of NBT-BT6-x%CeO2 ceramics was also examined.During the synthesis process of NBT-BT6-x%CeO2 powders, it was found that the mole ratio of citric acid to the total metal cations content (abbreviated as C/M) and pH value are the main contributing factors to the formation of the sol and gel. It was ascertained that a C/M in the range of 1.1-1.5 and a pH value in the range of 6-9 produced homogeneous, transparent sol and gel. NBT-BT6-x%CeO2 superfine powders with a pure perovskite structure were derived from the gel by calcining at 650 ℃ for lh.The influence of poling process on the piezoelectric properties of NBT-BT6-0.6%CeC>2 ceramic specimens was investigated. It was found that the piezoelectric properties of NBT-BT6-0.6%CeO2 ceramic specimens highly depend on poling field and temperature, while no remarkable effect of poling time on the piezoelectric properties was detected. A poling field of 3.0kV/mm, a poling temperature of 60℃ and a poling time of 15 min were ascertained to be preferred for NBT-BT6-x%CeO2 ceramic specimens.The piezoelectric and ferroelectric properties of NBT-BT6-x%CeO2 ceramic specimens were investigated. A pure perovskite structure was identified for NBT-BT6-x%CeO2 ceramics (C/M=1.3, pH=7.5), with CeO2 forming NBT-based solid solution with NBT-BT6. With the addition of CeO2, the piezoelectric constant (d33), electromechanical coupling factor (kp) and dielectric constant (ε 33T/ ε 0) are increased while the dissipation factor (tan δ) is obviously decreased. An obvious improvement on the piezoelectric properties was yielded at x=0.6. The piezoelectric constant enhances from 142 pC/N for NBT-BT6 ceramic specimen to 157pC/N for NBT-BT6-0.6%CeO2 ceramic specimen, while the electromechanical coupling factor from 27.0%to 31.2% and the dissipation factor is decreased from 4.20% to 2.72%. The electrical properties of NBT-BT6-x%CeO2 ceramic specimens apparently degrade when the addition of CeO2 was excessively increased above x=0.6. At room temperature the ferroelectric characteristics of NBT-BT6-x%CeO2 ceramic specimens were investigated with respect to their hysteresis loops. Saturated hysteresis loops were observed in the range of x=0-0.6, showing strong ferroelectric properties. The NBT-BT6-0.6%CeO2 ceramic shows a relatively large remanent polarization (Pr =38.0 μ C/cm2) and a relatively low coercive field (Ec=37.4kV/cm). The hysteresis loop deforms slightly when x=0.8. Saturated hysteresis loop could not be obtained when x=1.0.The influence of sintering temperature on the piezoelectric and ferroelectric properties of NBT-BT6-0.6%CeO2 ceramic specimen was investigated. It was observed that the increases of sintering temperature enhanced the piezoelectric and ferroelectric properties of NBT-BT6-0.6%CeO2 ceramic, which can be attributed to the development of grain growth and microstructure densification. With respect to the sintering behavior and electric properties, the sintering temperature in the range of 1130-1170 ℃ was ascertained to be preferred for NBT-BT6-x%CeO2 ceramic specimens.
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