熱電材料因為具備直接將廢熱轉換成電力的能力，因此受到廣泛的關注。近年來，熱電材料研究的復甦更進一步提升了熱電材料品質因數(ZT)，甚至已經充分探索的材料也有大幅度地提升。其中CoSb3屬方鈷礦尤其獲得許多的關注，因其具有熱電材料中特別優異的熱電性能、機械性質、熱穩定性以及環境友善性。而方鈷礦具有卓越的熱電性能，主要可以歸因於填充在空隙空間中的填充原子所導致的低導熱性。除此之外，降低熱導電性的方式也可以藉由藉由改變材料的聲子光譜進行，例如利用IV–VI族組對扭曲矩形的氮族環。雖然目前已經清楚熱電材料若要獲得高ZT值需要具備低熱導性，但是三元方鈷礦的本質電子結構與熱電性能之間的關係，經常被低估或完全忽略。因此本論文將會藉由結合實驗與計算的結果，對於高熱電性能的Co(Ge0.5Te0.5)3屬的三元方鈷礦進行深入的探討。此研究成果發現高ZT值不只與主能帶有相關，與次導電帶的載子傳輸也有直接的關聯，在確立了三元方鈷礦的優異熱電性質起源之後。本研究論文也進一步探討如何實現精細控制CoSn1.5Te1.5-x屬三元方鈷礦中的載子性質。並發現可以藉由化學方式調控結構中的四元Sn2Te2環，並發現主要載流子不只侷限於電子或電洞所組成。研究結果更進一步使用理論計算以及各式的光譜技術如X射線光電子能譜、X射線吸收光譜來探討半導體的導電特性。研究成果最終可藉由Ni與Co原子置換方式提升70倍的ZT值。;Thermoelectric materials have received a lot of attention because of their ability to convert waste heat directly to electricity with no moving parts. A resurgence in thermoelectric research has resulted in significant improvements in the thermoelectric figure–of–merit, zT, even for well-studied materials. CoSb3-based skutterudites stand out among thermoelectric materials for their excellent thermoelectric performance, robust mechanical properties, thermal stability, and environmentally friendly compositions in both space and terrestrial applications. Skutterudite material’s thermoelectric excellence is primarily attributed to its low thermal conductivity as a result of the addition of filler atoms (R) into the void space. An alternative approach for lowering thermal conductivity is to distort the rectangular pnictogen (Sb4) rings with group IV–VI pairs because the vibrations of the latter dominate the phonon spectrum of binary skutterudites. Although low thermal conductivity is necessary for high zT, the intrinsic electronic structure in ternary skutterudites is frequently understated or ignored entirely. The electronic origin of the high thermoelectric performance of Co(Ge0.5Te0.5)3-based ternary skutterudites is investigated in this thesis by combining experimental and computational studies. The high zT was demonstrated to be a direct result of the carrier transport contribution from a secondary conduction band, in addition to the primary band. After establishing the electronic origin of high thermoelectric performance in ternary skutterudite, the thesis moves to elaborate on how to achieve a fine control of carriers in ternary skutterudite like CoSn1.5Te1.5−x. It is found that the dominant carrier could be either electrons or holes via chemically tuning the quaternary Sn2Te2 rings in the structure. Both theoretical calculation and different spectroscopic probes, such as X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) were employed to unveil the conduction type switching details. On the other hand, a Ni-for-Co substitution ultimately led to a 70-fold increase in the dimensionless figure-of-merit (zT) at 723K.
