熱電材料能夠直接轉換熱能及電能，適合廢熱回收及無震動冷卻方面之應用。然而受限於其轉換效率不佳及製造成本過高，一直以來始終無法被廣泛地使用。近年來隨著優化熱電傳輸性質之相關理論被提出及材料製造技術的發展，熱電轉換效率已有所突破。從這些突破性的研究中可以了解到，為能夠達到熱電傳輸性質的有效調整，材料微結構的控制及調整是相當有效且重要的。電流輔助燒結是一常見的熱電材料製備方法，為瞭解高密度電流是否可改變材料內部微結構，並影響其熱電傳輸性質，本研究藉由自行設計組裝的電流輔助熱壓系統，分別製備碲化銻鉍(Bi0.4Sb1.6Te3)熱壓及電流輔助熱壓試片以進行比較。在以低電流密度直流電輔助燒結的試片中，試片呈現較佳的載子遷移率並維持低晶格熱傳導係數。藉由Mayadas-Shatzkes模型的理論分析，經過電流輔助燒結的界面具有較小的載子反射係數，意味著經電流輔助燒結後的界面對載子的傳輸具有較小的阻礙。而在此同時，不變的晶格熱傳導係數顯示聲子仍有效地被這樣的界面所散射。在以高電流密度脈衝電流輔助燒結的試片中，試片仍呈現較佳的載子遷移率並維持相同的晶格熱傳導係數。然而，微結構上，電流輔助燒結的試片呈現相當明顯的晶粒成長且有許多Sb奈米析出相在晶界上析出。藉由Callaway模型的分析，這些散佈於晶界上的Sb析出能夠降低晶格熱傳導係數，使得導電率在因晶粒成長而上升的情況下，仍能維持低的晶格熱傳導係數。總結來說，電流輔助燒結確實有效改變碲化銻鉍材料系統界面結構且造成奈米等級Sb析出相，達到提升熱電材料電導率但降低熱傳導係數的目的。

Thermoelectric materials that enable the direct conversion of thermal energy into electricity are promising for applications of waste heat harvesting and vibrationless cooling. However, poor conversion efficiency and high manufacturing costs appear to be major limiting factors for large-scale thermoelectric applications. In recent years, some intriguing breakthroughs in thermoelectric development have been reported with the new transport theories proposed and the advancement of material processing techniques. These groundbreaking works suggest that microstructrual manipulation is effective in modulating transport properties of thermoelectric materials. Among various processing techniques, current-assisted sintering is commonly employed to prepare thermoelectrics. This study intends to investigate the effect of high-density electric current on the evolution of microstructure and transport properties of thermoelectric material. A current-assisted hot-press system is designed and used to prepare hot-pressed and electrically-sintered Bi0.4Sb1.6Te3 samples. The samples sintered under low direct-current density exhibit enhanced carrier mobility and maintain low lattice thermal conductivity. According to Mayadas-Shatzkes model, the boundary in electrically-sintered sample reveals a smaller reflection coefficient, indicating that the boundary is beneficial for carrier transport with less hindering. The retained low lattice thermal conductivity suggests that the boundary prepared remains effective in blocking phonon transport in the electrically-sintered samples. Alternatively, the samples sintered with high pulse-current density also possess enhanced mobility and low lattice thermal conductivity. However, they reveal obvious grain growth and nanoscale Sb precipitates at grain boundaries. According to the modified Callaway model, these Sb precipitates tend to scatter phonons preferentially and lead to reduction in lattice thermal conductivity. Therefore, low lattice thermal conductivity is remained when electrical conductivity is increased due to grain growth. In conclusion, a high-density electric current indeed modulates the boundary structure and motivate Sb nano-precipitation in Bi0.4Sb1.6Te3 compounds, leading to increased electrical conductivity and reduced lattice thermal conductivity simultaneously.

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