目前已知同時具有高導電率、高強度和化學穩定性以及成本便宜的實用導電陶瓷材料,其實為數相當稀少。本論文主要針對鈦酸鋇(BaTiO3,以下表示時簡稱BT)添加氧化釔(Y2O3)或是Zr3Y(97mol.% ZrO2 + 3mol.% Y2O3)之鈦酸鋇陶瓷之導電現象研究,並找出使鈦酸鋇具有導電性需要之添加成分範圍和所需製程。在鈦酸鋇系統中,添加不同含量之Y2O3至鈦酸鋇中,或是添加不同含量之Zr3Y至鈦酸鋇中。製程方面皆採用一般常見之乾壓製程,燒結溫度範圍為1340℃-1500℃之間,觀察不同含量之添加物及燒結溫度不同會如何影響鈦酸鋇之導電性質。並找出可以使鈦酸鋇具導電性質所需添加之摻雜劑(Dopant)含量範圍,建立一個完整的成分和製程系統。即找出在低溫時,具有導電性質之鈦酸鋇導電陶瓷,例如鈦酸鋇添加Zr3Y之系統中,Zr3Y之添加量需在1-5wt% 間。和能夠表現出導電性所需之燒結溫度。並從所有可導電和不導電的成分中,各挑選二種成分,針對其導電的機制做進一步之分析。 在鈦酸鋇添加Y2O3之系統中,添加量低之BT-0.1wt%Y2O3系統,其導電性明顯優於一般之鈦酸鋇陶瓷,但是當含量增加至1wt% Y2O3時,導電性又回復到一般之介電材料之高電阻率,導電性差之絕緣體性質。而添加Zr3Y系統,BT-0.5wt% Zr3Y系統之導電性類似BT-1wt% Y2O3系統之絕緣體性質,電阻率高,導電性差。然而當添加Zr3Y至5wt% 時,BT-5wt% Zr3Y系統之導體現象又再次出現,導電性質和BT-0.1wt% Y2O3類似,由此可知,測量其電性發現,只要有添加Y2O3成分,即有可能出現導電性,但含量過少或是過多,都會使得導電性消失,在添加Zr3Y之鈦酸鋇系統中也是如此。 由於試片添加摻雜物之含量較低才能出現導電性,像是BT-0.1wt% Y2O3和BT-5wt% Zr3Y,因此在XRD、SEM、或是TEM分析上,無法找到以Zr或是Y為基底之第二相。因此,設計了其他有關電性方面的實驗,像是高溫導電或是同樣燒結溫度但改至還原氣氛下燒結以觀察其電性方面性質的改變,當試片改至還原氣氛下燒結時,通的是95% 氮氣+5% 氫氣,由於試片外環境的氧含量過低,內部之氧會擴散至外部,因此從缺陷方程式可以知道會產生氧空缺,留下自由電子。且添加之釔因為離子大小可同時取代鈦酸鋇中之鋇或是鈦原子。當替代了BaTiO3中之A-site(Ba site),為正三價之釔取代了正二價之鋇,使得材料多帶正電,因此會多出自由電子,屬於donor-doped BaTiO3,這種由donor-doped產生導電性主要是利用多餘的自由電子來產生導電性(n-type conductivity),因此在還原氣氛下燒結之試片,再次量測電性時,會發現在還原氣氛下燒結之試片,其導電性明顯提升。 相對地,BT-0.5wt% Zr3Y成分,在換算過後,其氧化釔的含量為所有試片中最少,經過高溫燒結後,並不具導電性,推論為在添加時,釔佔據在BaTiO3中之B-site(Ti site),由正三價取代正四價,造成材料帶負電,因此會產生電洞來補償,電洞仍能使得材料的導電性提升(p-type conductivity),此種鈦酸鋇稱為acceptor-doped BaTiO3, 但由於acceptor-doped造成之導電性需要較高的能量才能躍遷,因此在室溫時,熱活能(thermal energy)較低,電洞無法克服束縛,所以導電性沒有表現出來,經由高溫導電實驗發現,BT-0.5wt% Zr3Y之試片,的確有隨著溫度的上升使得導電性跟著提升。而另一不導電之成分為BT-1wt% Y2O3, 當添加過量的氧化釔時,可能會使得導電機制再次回到室溫時不會表現的電洞導電機制(p-type conductivity),所以添加過量時,導電性沒有隨添加的含量增加而提升,經由高溫導電實驗可知,當升高溫度時,的確會造成材料之導電性提升。因此有關探討鈦酸鋇陶瓷中導電的機制,回歸到最原始之電子電洞理論,和材料中之缺陷有極大的關係。
The conductivities of barium titanate (BaTiO3) systems doped with yittrium oxide (Y2O3) and Zr3Y (97mol.% ZrO2:3mol.%Y2O3)are studied in this thesis. Different amounts of Y2O3 and Zr3Y were added to study their influences on conductivity. Conventional oxide-mixing methods were adopted to produce the BaTiO3-based ceramics. The sintering temperature for the ceramics was varied in between 1340-1500℃ to study the influence of sintering temperature on conductivity. For the Y2O3-doped BaTiO3 system, the conductivity is at the highest when the BaTiO3 is doped with 0.1wt%Y2O3. The conductivity decreases significantly when the Y2O3 content increases to 1wt%. For the Zr3Y-doped BaTiO3 system, the conductivity with 5wt%Zr3Y doping is similar to that with 0.1wt% Y2O3 doping. Furthermore, if the Zr3Y doping is less than 0.5wt%, the conductivity is low. It is therefore concluded that in both the Y2O3-and Zr3Y-doped BaTiO3 systems, the dominant factor for the conductivity is the amount of yittrium doping. The origin of conductivity for the Y2O3-and Zr3Y-doped BaTiO3 system is investigated by studying the evolution of conductivity at different temperatures and reducing atmospheres. Donor-doped and acceptor-doped BaTiO3 systems are therefore defined. It is found that the room-temperature conductivity of BaTiO3 is governed by the amounts of its chemical defects, such as free electrons, electron holes, oxygen vacancies, and cation vacancies.