熱電材料能進行熱能和電能間之直接轉換，可運用在發電及致冷元件上。在所有熱電材料系統中，碲化鉍系化合物為室溫範圍下效率最佳的熱電材料。摻雜鍺的碲化鉍系統能提升工作溫度範圍到高溫端，並隨著鍺摻雜量的增加，主導缺陷從提供電洞載子的Bi_Te^(-1)及Ge_Bi^(-1)轉變成提供電子載子的Ge_i^(+1)及V_Te^(+2)，使得傳輸特性從p型半導體(Bi39Ge1Te60)轉換成n型半導體(Bi36.25Ge5Te58.75)。本研究係將摻雜鍺之碲化鉍化合物，熔煉過後再利用電流輔助熱壓製程製備樣品。本實驗發現在熱壓退火製程中，藉由改變施加的電流模式會使摻雜鍺之碲化鉍化合物有不同的微結構樣貌。對於Bi36.25Ge5Te58.75組成的試片，在熱壓退火時施加直流電模式會在材料內部產生多種析出相，包括Ge3Bi2Te6、Ge1Bi2Te4、Ge1.5Bi2.5Te5及BiTe。當電流轉換成脈衝模式後，發現析出物尺寸有下降的現象產生。另一方面，在施加交流電模式下試片會有Ge1Bi4Te7及Bi2Te3析出相所組成的層狀微結構產生。藉由調控電流模式產生不同的微結構，探討在鍺摻雜碲化鉍化合物系統熱電傳輸性質之影響為本研究的重點。研究結果發現，由於析出物尺寸過大，其本身性質特性的影響大於層狀結構間的散射效應，將主導整體材料的熱電性質，導致傳輸性質上並無更好的表現，對於微結構上只存在鍺摻雜碲化鉍單相的退火製程樣品，其在高溫573 K下具有最佳的熱電性質，熱電功率因子(PF)及熱電優值(zT)分別可達1.1 mW/mK2與0.52。

Thermoelectric (TE) materials enable the direct conversion between thermal and electrical energy for power generation and refrigeration applications. Among a variety of TE materials, Bi2Te3-based compounds are the most efficient TE materials near room temperature regime. Ge-doped Bi2Te3 is suitable for high operation temperature. With the increase of Ge-doping content, the dominant defect types change from electron acceptors (Bi_Te^(-1), Ge_Bi^(-1)) to electron donors (Ge_i^(+1), V_Te^(+2)), leading to a shift of conduction mode from p-type (Bi39Ge1Te60) to n-type (Bi36.25Ge5Te58.75). In this study, the solidified Ge-doped Bi2Te3 compounds were pressed at high temperature with the simultaneous passage of electric current, denoted as current-assisted hot-pressing (CAHP) process. We found that the Ge-doped Bi2Te3 compounds show distinct microstructure features by changing the electric current mode applied during the CAHP process. Gross formation of different precipitate phases including Ge3Bi2Te6, Ge1Bi2Te4, Ge1.5Bi2.5Te5 and BiTe has been observed in the Bi36.25Ge5Te58.75 matrix when a direct-current was applied during the CAHP process. The precipitate size was found to decrease by changing the direct-current mode into pulse-current mode. On the other hand, a lamellar structure of Ge1Bi4Te7 and Bi2Te3 phases was observed when an alternative-current is applied during the CAHP process. The effect of current-modulated precipitation on thermoelectric transport properties of the Ge-doped Bi2Te3 compounds is the subject of interest. The results show that the precipitate size is so large as to have minimal impact on phonon and electron scattering at interfaces. Instead, the transport properties of precipitates play a dominant role in apparent thermoelectric properties of the composite materials. The thermally annealed Ge-doped Bi2Te3 possesses a thermoelectric power factor of 1.1 mW/mK2 with a peak zT value of 0.52 at 573 K.

摘要 I
Abstract II
致謝 III
目錄 V
圖目錄 VIII
表目錄 XI
壹、緒論 1
1.1 研究背景 1
1.2 研究動機 5
貳、文獻回顧 6
2.1 碲化鉍化合物 7
2.1.1 碲化鉍材料之晶體結構 7
2.1.2 碲化鉍材料之晶格缺陷 8
2.2 鍺摻雜碲化鉍(Ge-doped Bi2Te3)系統 10
2.2.1 鍺摻雜碲化鉍之析出相 10
2.2.2 鍺摻雜碲化鉍之晶格缺陷 12
2.2.3 碲化鍺-碲化鉍(GeTe-Bi2Te3)系統之層狀結構及性質 13
2.3 碲化鉍系統熱電材料的發展 18
2.3.1 火花電漿燒結製程 18
2.3.2 電流輔助熱壓退火製程 20
參、實驗流程及分析方法 23
3.1 試片製備 25
3.2 晶相分析 28
3.2.1 表面形貌、析出物及成分分析 28
3.2.2 X光繞射分析 28
3.3 量測方法 29
3.3.1 Seebeck係數與四點式電阻率量測 29
3.3.2 熱傳導係數量測 31
3.3.3 霍爾效應量測 32
肆、結果與討論 34
4.1 熔煉及退火製程之微結構、缺陷機制及傳輸性質探討 34
4.1.1 鍺摻雜量及退火製程對鍺摻雜碲化鉍化合物微結構的影響 35
4.1.2 鍺摻雜量及退火製程對鍺摻雜碲化鉍化合物電性和缺陷種類的影響 37
4.1.3 鍺摻雜碲化鉍化合物熱電性質隨溫度變化量測結果 41
4.2 經電流輔助熱壓退火製程之鍺摻雜碲化鉍化合物微結構及傳輸性質探討 45
4.2.1 電流模式差異對鍺摻雜碲化鉍化合物微結構的影響 46
4.2.2 經電流輔助熱壓退火製程之鍺摻雜碲化鉍化合物熱電性質隨溫度變化之量測及計算結果 52
4.2.3 析出相對Bi36.25Ge5Te58.75試片整體性質影響之評估 55
4.3 鍺摻雜碲化鉍化合物層狀析出物生成機制探討 57
4.3.1 固化速度快慢對樣品缺陷數目的影響 57
4.3.2 起始熔煉試片缺陷數目對微結構的影響 59
4.3.3 原子受電流遷移路徑及析出物生成順序 62
4.4 經球磨加電流輔助熱壓燒結製程之鍺摻雜碲化鉍化合物微結構及傳輸性質探討 66
4.4.1 球磨製程對Bi36.25Ge5Te58.75材料微結構的影響 67
4.4.2 球磨製程對Bi36.25Ge5Te58.75材料主導缺陷的影響 69
4.4.3 經球磨製程之Bi36.25Ge5Te58.75材料熱電性質隨溫度變化之量測 70
伍、結論 73
陸、參考文獻 75

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