Bi1.7+xSb0.3-xTe2.7Se0.3+y wt%Te x=0、0.05、0.1 y=15、20、25 熱電性質研究

Abstract

隨著21世紀的來臨，能源議題逐年被重視，許多新興材料以及相關研究課題正如火如荼進行中，其中之一的熱電材料，著眼於其無須透過機械裝置的耦合而可達到熱能與電能的直接互相轉換，近20年來不斷地被研究，其中Bi2Te3 因為其ZT最大值落在300~500 K之間，對於室溫範圍具有應用潛力，因此本論文之研究課題以Bi1.7Sb0.3Te.27Se0.3為基礎尋找具高熱電轉換效率之n型合金塊材，透過Sb及過量的Te參雜量的調制(Sb: 0.05-0.1, Te: 15-30wt%)，尋找最佳熱電轉換效率之熱電材料，並研究不同的製程方式對ZT值的影響，分別使用布里奇曼法(Bridgman-Stockbarger Method)、高溫燒結(Furnace melting)、火花電漿燒結 (SPS)製備樣品，研究不同參雜比例對熱電性質的影響，製備之樣品以X光繞射儀(XRD)分析結晶相，X-光螢光分析儀 (XRF)確認元素成分比例，ZEM-3分析導電係數以與席貝克係數，並探討以上物理量、材料特性與不同長晶方法及成分之間的關係，以高溫燒結製備之Bi1.75Sb0.25Te2.7Se0.3樣品為參考，其材料優質係數ZT約為0.55， 而Bi1.75Sb0.25Te2.7Se0.3+15wt%Te使用布里奇曼法在750度每小時5 mm的長晶速率所製備之塊才其ZT則最高可達0.84，而火花電漿燒結系統在380度50 MPa的條件下所得到的材料其ZT值則達0.8，相較於Bi1.75Sb0.25Te2.7Se0.3之樣品均有顯著提升，添加Sb與Te確實可有效提升zT值，然而當Te添加量過多，zT值不升反降，研究結果顯示Te添加量不應超過20wt%,。

At the start of the 21st century, energy issues have been paid attention year by year, as a potential solution for saving energy, thermoelectric materials have attracted a lot of study in the past 20 years. Among thermoelectric materials, Bi2Te3, because its maximum ZT value falls between 300 and 500 K makes it a high application potential near the room temperature range. Therefore, we are interested in if the Bi2Te3-based materials can be tuned to even improved advance. This work focused on the n-type materials Bi1.7Sb0.3Te2.7Se0.3, looking for n-type alloy bulk materials with high thermoelectric conversion efficiency by doping level tuning of Sb and Te (Sb: 0.05-0.1, Te: 15-30wt%). Meanwhile, three synthesize methods Bridgeman-Stockbarger Method, Furnace melting, spark plasma sintering (SPS) are employed to study the influence of the method on the ZT values and effects on thermoelectric properties. The prepared samples are analyzed by X-ray diffractometer (XRD) and X-ray fluorescence analyzer (XRF) for identification of crystalline phases and the atomic ratio. The ZEM-3 and LFA are employed to study the electrical conductivity and Seebeck coefficient, and thermal conductivity, respectively. Taking the Bi1.75Sb0.25Te2.7Se0.3 sample that is prepared by the pre-melting method as a reference, the material figure of merit ZT is about 0.55. While the maxima ZTs of Bi1.75Sb0.25Te2.7Se0.3+15wt%Te that prepped by the Bridgman method (growth rate of 5 mm/hr at 750 degrees) and by the spark plasma sintering system (at 380 degrees 50 MPa) are reached up to 0.84 and 0.8, respectively. Which are significantly higher than that of the Bi1.75Sb0.25Te2.7Se0.3. However, the zT suppressed at high tuning level, which indicates that the Te tuning shall not higher than 20wt%.