探討三價離子摻雜於電解質BaZrO3的導電趨勢

Abstract

利用實驗研究不同三價摻雜金屬BaZr0.9M0.1O3-α (M3+ = Al3+、Ga3+、In3+、Y3+、La3+ 、Nd3+、 Sm3+、Gd3+、 Dy3+、Ho3+ 、Er3+)的離子導電趨勢。 實驗先利用溶膠-凝膠法(sol-gel)加入添加物NiO並以NH4OH調控溶液pH值的方式改良合成BaZr0.9M0.1O3-α的粉末，之後在壓錠燒結高溫獲得樣品。在各種的合成變因，像是添加物的比例、pH值、改變燒結溫、增加球磨過程，有系統的測試以達到更高的密度、較大的晶粒尺寸和更好的質子導電率。分別利用Archimedes測量法、XRD、SEM、EDS鑑定樣品密度、化學成分、顯微結構和摻雜比例，進行實驗前後的樣品分析。 BaZr0.9M0.1O3-α是質子導體藉由摻雜產生氧空穴，在含有水氣的環境下，氧空穴與水氣結合獲得質子，探討質子的傳導。實驗利用DC二電極和AC四電極的EIS在飽和水氣的氮氣下進行質子導電率的測試，測量溫度為100-700℃。探討在相同條件下，摻雜金屬對質子導電率的影響與趨勢，並進一步對各摻雜金屬以Arrhenius方程式得到activation energy與pre-exponential factors。 實驗結果顯示質子傳導與摻雜半徑有關，較小的摻雜金屬離子有較弱的水合能且質子濃度較低，造成較低的質子傳導。而較大的摻雜金屬離子會導致A-site摻雜的問題，造成氧空穴減少，得到較差的質子導電率。最適當的摻雜金屬離子(Ho3+、Er3+、Dy3+)擁有最好的質子導電率。

This thesis reports the trends of proton conductivity on series of trivalent cations (Al3+, Ga3+, In3+, Y3+, La3+ Nd3+ Sm3+, Gd3+, Dy3+, Ho3+ and Er3+) doped BaZrO3. The ceramic powders are initially synthesized by sol-gel method with small amount of NiO additive and pH-controlled condition and subsequently compressed to pellet sintered at higher temperature. Various synthetic parameters, such as ratios of additives, pH values, sintering temperature, ball mill processes, have been systematically examined to achieve the higher density, larger grain size and better proton conductivity. The desnity, chemical composition, microstructure and dopant ratios of samples are characterized by Archimedes measurement, XRD, SEM, EDX, respectively. The protonic conductivity is measured by DC 2-electrode and AC 4 electrode methods from 700–100℃ in the wet-N2 condition and further analyzed in the Arrhenius equation to determine the corresponding activation energy and pre-exponential factors for each cation-doped BaZrO3. The result shows that proton conductivity is radius dependent for the doped cations. Smaller trivalent cations will have weaker hydration energy and give smaller proton concentration, thus, result lower proton conductivity. On the other hand, larger cations will cause A-site doping problem and give less oxygen vacancy, therefore, show poor proton conductivity. As a result, the cations of Ho3+, Er3+ and Dy3+ with suitable radius will give the best proton conductivity.