無鉛鐵電陶瓷BaTiO3系統與Bi1/2Na1/2TiO3系統 鐵電性與顯微組織的研究

The investigations of ferroelectric properties and microstructure for lead-free ferroelectric ceramics BaTiO3 system and Bi1/2Na1/2TiO3 system

吳國彰(Guo-Zhang Wu)

指導教授 ： 謝宗霖

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.01924

摘要

本論文主要針對BaTiO3及Bi1/2Na1/2TiO3兩種無鉛鐵電陶瓷進行研究。在BaTiO3系統中，添加不同比例的ZrO2，並利用兩種製程來製備；而Bi1/2Na1/2TiO3系統，分為三個部份，先探討Bi1/2Na1/2TiO3/ BaTiO3/ Bi1/2K1/2TiO3三元相圖中，兩相共存區域（MPB）成分性質的分析；之後在選定的組成中，添加不同的摻雜劑對性質的影響；最後則是探討在MPB區域內、外，其性質有何不同。
鈦酸鋇添加氧化鋯系統，其電滯曲線的表現隨氧化鋯的增加而變差，無論是乾壓製程或膠粒製程，都呈現相同的結果。顯微組織方面，兩種製程有明顯的差異，由SEM觀察可以知道膠粒製程會有比較好的緻密性，而乾壓製程的孔洞偏多；添加量為5 wt%時已有第二相出現，由XRD與TEM-DP可以知道第二相為Ba6Ti17O40。而TEM有觀察到core-shell結構，且Zr4+量越高，內部應變能及差排堆疊的情形皆增加。
Bi1/2Na1/2TiO3方面，首先比較BNBT x、BNKT y、BNBK x-y（x＝6、6.5、7，y＝16、18、20）系統，可以知道BNBT x擁有很強的鐵電性，BNBK x-y則是有較高的去極化溫度。在BNBK x-y中，BNBK 6.5-20有最小的矯頑電場，所以被選為添加摻雜劑的組成，可以知道添加Mn2+、Co3O4可以使電滯曲線放大，添加La3+、Nb5+則會使鐵電性消失。而在MPB內、外的研究，選取相圖上菱體對稱的BNBK 90/5/5與正方對稱的BNBK 75/5/20，與MPB內的BNBK 6.5-20、BNBK 7-20來做比較，可以知道BNBK 90/5/5鐵電性表現不錯，但對溫度相當敏感；而BNBK 75/5/20的鐵電性表現不佳，但在較高溫度可以保留較多的極化量。

關鍵字

無鉛鐵電材料 ； 鈦酸鋇 ； 鈦酸鉍鈉 ； 蝴蝶曲線 ； 電滯曲線

並列摘要

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.

並列關鍵字

lead-free ferroelectric ； barium titanate ； bismuth sodium titanate ； butterfly loop ； hysteresis loop

參考文獻

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