碲化鉛系化合物為中高溫區段常見之熱電材料，具有將廢熱回收的潛力，一般常見的製備方式採取熱壓成形，近期的研究則改用火花電漿燒結法，試圖提升碲化鉛之熱電優值。然而，電流效應對碲化鉛內部晶體缺陷或材料微結構的影響，尚未完全了解。本研究藉由電流輔助燒結的方式製備碲化鉛塊材，並與傳統熱壓燒結或布里奇曼製程所得之材料相比較，嘗試探討電流對碲化鉛內部原子的影響及熱電傳輸性質的差異。本實驗所採用電流輔助燒結技術可將碲化鉛製程溫度從常見的400 ℃降低至300 ℃，並且相對密度可達97.9%。研究結果指出電流輔助燒結所製備之碲化鉛材料內部的鉛原子會受電流驅使，造成電致遷移的現象，並在晶體內部產生大量空位缺陷。與熱壓試片相比，室溫的載子濃度從5.27 * 10^17 cm^-3增加到2.09 * 10^18 cm^-3；載子遷移率則因為晶粒成長與界面燒結狀況改善，導致其值由390 cm^2/V*s 提高到674 cm^2/V*s。而電導率的大幅提升，使碲化鉛材料熱電功率因子可在323 K達到1.66 mW/m*K^2。另外，對於碲化鉛之高溫傳輸行為，本研究亦根據波茲曼傳輸方程式，考量不同能帶結構與溫度的關係，估算碲化鉛材料的Seebeck係數隨溫度變化之情形。

Lead telluride is a classical thermoelectric material suitable for thermal energy harvesting at middle-high temperature regime. Besides typical hot-pressing technique, spark plasma sintering is commonly employed in fabricating quality lead telluride compounds. Nevertheless, how electric current affects lattice defects and microstructure of lead telluride is still not fully understood. In this study, we intend to investigate the current-induced lead migration and its impact on thermoelectric transport properties of lead telluride prepared by current-assisted sintering method. The process temperature is effectively lowered to 300 ℃ with the relative density up to 97.9%. The results indicate that the lead atoms are motivated under an electric field by forming many Pb vacancies in lead telluride. The carrier concentration of electrically sintered PbTe at room temperature is 2.09 * 10^18 compared to the hot-pressed PbTe with a value of 5.27 * 10^17 cm^-3. The carrier mobility increases from 390 cm^2/V*s. to 674 cm^2/V*s with the help of electrical sintering. Moreover, the electrically sintered PbTe demonstrates a large thermoelectric power factor of 1.66 mW/m*K^2 due to the greatly enhanced electrical conductivity. In addition, we have calculated the temperature-dependent thermoelectric properties of lead telluride with a multivalence band structure according to the Boltzmann transport equation.

摘要 i
Abstract ii
致謝 iii
目錄 iv
圖目錄 vi
表目錄 viii
壹、緒論 1
1.1 研究背景 1
1.2 研究動機 4
貳、文獻回顧 5
2.1碲化鉛系化合物 6
2.1.1碲化鉛之電子結構 6
2.1.2碲化鉛之晶格缺陷 7
2.2 碲化鉛系熱電材料發展 8
2.2.1摻雜效應 9
2.2.2奈米結構效應 11
2.3 電流輔助粉末燒結製程 13
2.4 鉛原子電致遷移現象 15
參、實驗設計與理論方法 16
3.1 實驗流程 17
3.2 量測方法 19
3.2.1 Seebeck係數與四點式電阻率量測 19
3.2.2 霍爾效應量測 21
3.2.3 熱傳導係數量測 23
3.2.4 表面形貌、析出物、成分分析 25
3.2.5 X光繞射分析 25
肆、結果與討論 26
4.1 熱壓與電流輔助燒結試片比較 26
4.1.1 電流對碲化鉛載子濃度之影響 26
4.1.2 電流對碲化鉛載子遷移率之影響 29
4.1.3 通電時間對碲化鉛之電性與結構影響 32
4.1.4 電流對碲化鉛熱傳導係數影響 37
4.2 溫度對碲化鉛傳輸特性之影響 39
4.2.1多重能帶假設與經驗式 40
4.2.2變溫電阻率與Seebeck係數擬合結果與分析 43
伍、結論 46
陸、參考文獻 47

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