| 研究生: |
蕭名桓 Hsiao, Ming-Huan |
|---|---|
| 論文名稱: |
鈦過量對摻鑭鈦酸鍶塊材熱電性質之影響 Effects of Ti excess on thermoelectric properties of La-doped strontium titanate bulks |
| 指導教授: |
黃啟祥
Hwang, Chii-Shyang |
| 學位類別: |
碩士 Master |
| 系所名稱: |
工學院 - 材料科學及工程學系 Department of Materials Science and Engineering |
| 論文出版年: | 2018 |
| 畢業學年度: | 106 |
| 語文別: | 中文 |
| 論文頁數: | 96 |
| 中文關鍵詞: | 熱電材料 、鈦酸鍶 、鈦過量 |
| 外文關鍵詞: | Thermoelectric material, SrTiO3, Ti excess |
| 相關次數: | 點閱:88 下載:2 |
| 分享至: |
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隨著環保意識興起,新能源的開發及節能減碳,已經成為現今人類發展的重要議題。熱電材料透過溫差即可將熱能與電能轉換,為一受到期待的功能材料,在溫差發電及熱電致冷方面都具有廣泛的應用價值,其中陶瓷熱電材料具有成本低廉、無毒、無污染等之優點,是深具發展潛力的材料。
陶瓷材料中之鈦酸鍶是功能性非常多元的材料,具有介電常數高、介電損耗低、Seebeck係數高及熱穩定性好等之優點,是科學家積極研究的熱電材料。稀土元素的摻雜為提升鈦酸鍶熱電性質的常見手段,其中以鑭摻雜之鈦酸鍶在前人的研究中具有最佳熱電性質。此外,鍶與鈦的計量調整為改善鈦酸鍶熱電性質的一個新方向,當鈦過量時材料內會有第二相生成,進而影響鈦酸鍶的熱電性質。
因此,本研究以鈦過量的摻鑭鈦酸鍶為研究材料,實驗以固相反應法合成粉末,將粉體成型後於氬氫還原氣氛(5% H2-95%Ar)中以1500 ℃燒結4小時成為Sr0.92La0.08TixO3(x = 1.00 ~ 1.10) 塊材,並探討鈦過量塊材之結晶相、微結構、電傳導與熱傳導特性及熱電性質的影響。
結晶相與微結構方面,諸試樣均為鈦酸鍶單一相,鈦過量對晶粒大小無顯著影響,整體晶粒皆呈現近圓球狀,其平均粒徑大小為2 ~ 3 μm,塊材之相對密度為90 ~ 92 %。
電傳導率方面,隨著鈦過量的增加,電傳導率呈現先增後減之趨勢,顯示微量鈦過量有助於電傳導率之提升,1.04 Ti試樣具有最高之功率因子(Power factor),其值約為1.03 mW/m-K2。Seebeck係數方面,諸試樣皆為n型半導體,鈦過量對Seebeck係數影響不大。熱傳導率方面,隨著鈦過量的增加,電傳導率的提升,使得熱傳導率也隨之增加,故無鈦過量之1.00 Ti試樣具有最低之熱傳導率。
綜合各項熱電性質所計算之試樣ZT值,結果顯示鈦過量之諸試樣,其ZT值均高於無鈦過量之試樣,表示鈦過量是能有效提升摻鑭鈦酸鍶熱電性質的方法,1.04 Ti試樣具有最高ZT值,在673K時約為0.13。
In this study, the effects of Ti excess on the thermoelectric performance of La-doped strontium titanate bulks were investigated. Nonstoichiometric Sr0.92La0.08TixO3-δ (x = 1.00 ~ 1.10) powders were prepared by conventional solid-state reaction and calcined at 1300 °C for 6 hours with intermediate grinding. The mixture powders were CIP-ed and then sintered at 1500 °C for 4 hours in a 5% H2/Ar atmosphere. The densities of samples were evaluated by Archimedes’ method. The crystal structure and microstructure were confirmed by XRD and SEM, respectively. The thermoelectric properties of bulk samples were measured from 303 K to 673 K. Ti excess was found to have a noticeable effect on the electrical conductivity, but slightly decreased the absolute value of Seebeck coefficient. High power factor was observed in sample with appropriate Ti excess content. The thermal conductivity increased by Ti excess as electronic thermal conductivity increased. Consequently, Sr0.92La0.08Ti1.04O3-δ showed the highest the highest figure of merit (ZT)value of ~ 0.13 at 673 K.
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