| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 97 === The ferroelectric and dielectric properties of lead free ferroelectric ceramic 0.854(Bi0.5Na0.5)TiO3-0.026BaTiO3-0.12(Bi0.5K0.5)TiO3 (abbreviated as BNBK 85.4/2.6/12) doped with niobium (Nb) or lanthanum (La) are investigated in this study. The chosen doping amounts are: 0.1, 0.25, 0.5, 0.75, 1.0, 1.5 and 2.0 wt%. For ferroelectric properties, polarization switching is promoted with 0.1 wt% of doping (either Nb or La), and consequently, the shape of the hysteresis loop becomes more rectangular. However, as the doping amount or measuring temperature is further increased, the values of remnant polarization and coercive field decrease simultaneously, and the measured hysteresis curve transforms from a major loop into a double-loop and then eventually into a slim loop. For different doping amounts and measuring temperatures, macro-micro domain switching (i.e., proportions of order and disorder regions) is believed to be the mechanism which governs the ferroelectric behaviors of BNBK 85.4/2.6/12. The depolarization temperature of BNBK 85.4/2.6/12 is decreased by either Nb or La doping. The measured strain hysteresis data show that 0.75 wt% Nb-doped BNBK 85.4/2.6/12 ceramic exhibits an electrostrain of about 0.2% and an apparent d33 of 472 pC/N. It is potentially a candidate material for lead-free actuator applications.
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