| Sodium bismuth titanate, (Na0.5Bi0.5)TiO3 (NBT), is a kind of perovskite-type ferroelectric with a relatively large remnant polarization (Pr=38μC/cm2) at room temperature and a relatively high Curie temperature (Tc=320℃). For its strong ferroelectricity at room temperature, NBT has been considered to be a promising candidate material for lead-free piezoelectric ceramics. In this dissertation, conventional solid state reaction method, molten solid method and hydrothermal method have been employed to prepair NBT-based ceramics, and the synthesis and preparation, structural characteristics, poling process and piezoelectric properties of NBT-based ceramics have been investigated. The influence of the composition and structure on the piezoelectric properties has been studied. The relation between the ferroelectric nature and piezoelectric properties has been established in terms of experimental results.The [Bi0.5(Na1-x-yKxLiy)0.5]TiO3 power synthesis through molten salt method was investigated at a temperature range of 650 - 700°C for 2 - 4h in the present study. Power synthesis was also conducted through the conventional solid state reaction method at a temperature range of 750 - 900°C for 2 - 4h for comparison. The XRD results indicated that the favorable synthesizing temperature for molten salt method was 700°C, significantly lower than that for solid state reaction method, where a calcining temperature of 850°C was needed. Both the XRD and SEM results revealed better crystallization of the powders obtained through molten salt method, compared with those through the conventional solid state reaction method.A hydrothermal method had been employed to synthesize the NBT powders, the structural characteristics also had been investigated. It was found that the property of the Ti precursor contributed greatly to the crystallization of NBT powders. In the experiment, we chosed Ti(OC4H9)4, Bi(NO3)3·5H2O and NaOH as the titanium, bismuth resource and minerlizer respectively. It was ascertained that the hydrothermal temperature of 160°C, synthesis time of 24h, crystallizer concentration of 12M, and the pH values of 12-13 for precursors are preferred.The influence of poling process on the piezoelectric properties of NBT-based ceramic specimens was investigated. It was found that the piezoelectric properties of [Bi0.5(Na1-x-yKxLiy)0.5]TiO3 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 3.5kV/mm, a poling temperature of 80-90°C and a poling time of 20min were ascertained to be preferred for NBT-based ceramic specimens.The ferroelectric properties of NBT-based ceramics were investigated. The results confirm an essential relation between the ferroelectric nature and piezoelectric properties for NBT-based ceramics. Both the remanent polarization (Pr) and coercive field (Ec) affect the piezoelectric properties of the specimens. [Bi0.5(Na1-x-yKxLiy)0.5]TiO3 shows a typical ferroelectric polarization hysteresis loops. It can be revealed that the remanent polarization Pr of the sample remains about 30μC/cm2 by using the molten salt method. Meanwhile, a greatly decrease in the coercive field Ec is also observed, which facilitates the domain movement leading to an increase in piezoelectric properties. The piezoelectric charge constant d33 is increased from 110 to 160pC/N. It is concluded that the molten salt method can enhance the ferroelectrics and piezoelectric effect.
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