硫族化鉛(Lead Chalcogenide)為中高溫區段常見之熱電材料，其中硫化鉛又以低成本、高蘊含量而具新興取代碲化鉛之發展潛力。然而，硫化鉛受限於高熱導、低載子濃度的特性而在熱電表現上不甚理想。因此，本研究欲以多元合金效應與合金摻雜效應分別針對高熱導、低導電進行優化與探討。利用硒硫合金在室溫下的高互溶度形成無析出相之均勻固溶體，同時藉由晶格扭曲效應降低熱導率；另外藉由錫、鉍元素的摻雜進行能帶結構修正及載子濃度調升，用以改善導電率。實驗第一部分中，我們將硒硫化鉛針對不同的錫摻雜比例與熱壓製程參數進行嘗試，最終選定Pb0.45Sn0.05Se0.25S0.25作為標準比例與熱壓溫度550°C以達到最佳燒結緻密度來製作試片。第二部份則是探討錫元素在材料系統中的影響，內部結構對於陰、陽離子空位缺陷的平衡使其在極微量摻雜區間(Sn=1%)於室溫提升導電率，而後隨溫度增加與Pb0.45Sn0.05Se0.25S0.25無異。第三部份我們添加Bi元素提升其載子濃度，與Pb0.45Sn0.05Se0.25S0.25試片相比，室溫載子濃度從1.83·10^18 cm^(-3)增加到5.43·10^19 cm^(-3)，導電率由133.2 S∙m^(-1)上升至1289.6 S∙m^(-1)。因此最終熱電優值在573K下從純硫化鉛的0.165上升至0.430，數值有顯著的提升。

Lead Sulfide (PbS) has great potential as a substitute for lead telluride (PbTe) owing to its low-cost and earth-abundant features. However, high thermal conductivity and low carrier concentration of PbS causing relatively low thermoelectric performance compared with PbTe which limits its further application. This study aims to optimize and investigate the high thermal conductivity and low electrical conductivity separately through the effects of multi-element alloying and doping. We utilized the high mutual solubility of selenium and sulfur alloys to form a homogeneous solid solution without precipitation phase while introduced the lattice distortion effect to reduce thermal conductivity. Furthermore, the introduction of tin and bismuth elements was used to modify the band structure and enhance carrier concentration, thereby improving electrical conductivity. We have optimized the condition of sintering parameter to achieve great densification. Next, we explored the influence of tin elements in the material system. The equilibrium of anion and cation vacancy defects within a very low doping range (~1%) at room temperature contributed to an enhancement of the electrical conductivity, which converged with the standard sample (5%) as the temperature increased. Finally, we introduced bismuth to increase the carrier concentration. the room temperature carrier concentration was found to increase from 1.83∙10^18 cm^(-3) to 5.43∙10^19 cm^(-3), and the electrical conductivity raised from 133.2 S∙m^(-1) to 1289.6 S∙m^(-1). Consequently, the thermoelectric figure of merit increased significantly from 0.165 for pure PbS to 0.430 at 573 K, leading to a substantial enhancement in the thermoelectric performance.

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