The investigations of ferroelectric properties and microstructure for lead-free ferroelectric ceramics BaTiO3 system and Bi1/2Na1/2TiO3 system
Date Issued
2006
Date
2006
Author(s)
Wu, Guo-Zhang
DOI
zh-TW
Abstract
The lead-free ferroelectric ceramics of BaTiO3 system and Bi1/2Na1/2TiO3-based systems are studied in this thesis. The BaTiO3 system, with ZrO2 doping, is prepared by uniaxial dry pressing and colloidal processing methods. For the Bi1/2Na1/2TiO3-based systems, three areas are investigated: (1) the characteristics of the morphotropic phase boundary (MPB) compositions of a(Bi0.5Na0.5)TiO3-bBaTiO3- c(Bi0.5K0.5)TiO3 (abbreviated BNBK 100a/100b/100c) ternary system are studied; (2) the BNBK composition with the lowest coercive field (Ec) is doped with various hard and soft dopants; the effects of doping are examined; (3) the characteristics of the BNBK compositions inside and outside the MPB are compared.
In the BaTiO3 system, the remanent polarization (Pr) decreases with increasing ZrO2 doping amount. BaTiO3 ceramic bulks produced from the two processing methods, uniaxial dry pressing and colloidal processing, show different microstructures. SEM micrographs reveal that a denser microstructure is produced by the colloidal method. Ba6Ti17O40 second phase in ZrO2-doped BaTiO3 is detected by XRD and TEM-DP; the core-shell structure is observed by TEM-BF. Pile-up dislocations extend with increasing ZrO2 doping amount – an indication of an increase in internal stress.
In the Bi1/2Na1/2TiO3-based systems, (Bi1/2Na1/2)TiO3-BaTiO3 (BNBT) exhibits strong ferroelectric characteristics and BNBK shows a higher depolarization temperature. BNBK 88.1/3.9/8 has the lowest coercive field among the MPB compositions of BNBK, and is selected for doping examinations. The Pr and Ec of BNBK 88.1/3.9/8 increase with 1 mol% Mn2+ doping. In contrast, the ferroelectric behavior is hindered when La3+ and/or Nb5+ are added. In addition, BNBK 90/5/5 with a rhombohedral symmetry displays much more noticeable ferroelectric hysteresis characteristics than BNBK 75/5/20, a tetragonal symmetry, but its ferroelectricity is more susceptible to temperature fluctuation. Tests show that BNBK 75/5/20 can preserve more of its polarization than BNBK 90/5/5 at 110°C.
Subjects
無鉛鐵電材料
鈦酸鋇
鈦酸鉍鈉
蝴蝶曲線
電滯曲線
lead-free ferroelectric
barium titanate
bismuth sodium titanate
butterfly loop
hysteresis loop
Type
thesis
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