Thermoelectric Properties of Γ-Al2o3 Doped Bi-Sb-Te Materials

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Project title

Code/計畫編號

MOST105-2221-E019-012

Translated Name/計畫中文名

摻雜γ-Al2O3之Bi-Sb-Te熱電複合材料特性研究

Project Coordinator/計畫主持人

Pee-Yew Lee

Funding Organization/主管機關

National Science and Technology Council

Department/Unit

Department of Optoelectronics and Materials Technology

Website

https://www.grb.gov.tw/search/planDetail?id=11901427

Year

2016

Start date/計畫起

01-08-2016

Expected Completion/計畫迄

31-07-2017

Bugetid/研究經費

1146千元

ResearchField/研究領域

材料科技

"過去三十年，從事熱電材料研究的學者針對碲化鉍基化合物進行廣泛的研究以期能使其成為最佳的熱電材料，最近則有學者提出很多可增加此材料熱電優值的研究構思，依據此等構思而衍生出的一個有效方法是希望經由合金化、摻雜不同元素或引入複雜晶體構造的情形下，可同步增加此材料的導電率及降低其導熱率，藉此更加提升碲化鉍基化合物的熱電優值，根據此想法相關研究團隊乃以不同的球磨和成型方式，分別製備出CNTs/Bi0.4Sb1.6Te3 、 C60/(Bi,Sb)2Te3、Cu7Te4/Bi0.4Sb1.6Te3、BN/Bi0.4Sb1.6Te3、WO3/Bi0.4Sb1.6Te3、PbTe/(Bi,Sb)2Te3 等奈米複合材料塊材，其研究結果顯示添加CNTs 及C60 會使導熱率下降，故有利於 CNTs/Bi0.4Sb1.6Te3、C60/(Bi,Sb)2Te3 塊材之ZT 值的提升；Cu7Te4/Bi0.4Sb1.6Te3 塊材之ZT 值因 Cu7Te4 的添加使導電率增加，然而席貝克係數只有略微下降，使其功率因子能出現最大值； WO3/Bi0.4Sb1.6Te3 及BN/Bi0.4Sb1.6Te3 等塊材的ZT 值會因WO3 與BN 的添加使導電率急速下降而減少；而添加PbTe 之PbTe/(Bi,Sb)2Te3 塊材雖可提高其導電率，但因導電率與席貝克成反比，使席貝克係數大大地降低，進而使整體的ZT 值下降；以上研究結果顯示具奈米複合材料結構之奈米熱電複合材料塊材，其ZT 值會因添加不同的奈米顆粒而出現增加或減少的變化。最近有學者發現在n-型Bi2Se0.3Te2.7 熱電合金中添加1.0 vol. % γ-Al2O3 後，在400K 可得到 0.99 的最高ZT 值，較未添加γ-Al2O3 之Bi2Se0.3Te2.7 單相合金高約35%，此結果顯示在碲化鉍基熱電材料中添加γ-Al2O3 可有助於熱電性能的改善。而γ-Al2O3 是常用於製備金相試片的拋光用顆粒，與上述Bi0.4Sb1.6Te3 複合材料塊材中添加之CNT、C60、Cu7Te4 及PbTe 等粒子比較，是非常容易取得的材料，除此外更具有價格便宜的優勢，因此極適合取代此等奈米添加物粒子，摻雜至Bi0.4Sb1.6Te3 以製備Bi0.4Sb1.6Te3 複合材料塊材。但文獻調查發現，γ-Al2O3/ Bi0.4Sb1.6Te3 熱電複合材料塊材之研究至今仍無人進行，綜上所述，本研究之目的在探討利用粉末冶金技藝來製備具具微米/奈米複合材料結構之γ-Al2O3/Bi0.4Sb1.6Te3 熱電塊材的可行性，並進一步瞭解塊材的結構與熱電及機械性質的關聯性。研究工作之進行先利用高能量震動式球磨機製備出 Bi0.4Sb1.6Te3 合金粉末，接著將不同重量百分比的γ-Al2O3 粉末混合Bi0.4Sb1.6Te3 合金粉末後，再以同型之球磨機合成γ-Al2O3/Bi0.4Sb1.6Te3 複合材料粉末，最後利用真空熱壓技術將此複合材料粉末製備成複合材料塊材，所製備之複合材料粉末與塊材將依序分別以X 光繞射儀、SEM 掃瞄式電子顯微鏡、TEM 穿透式電子顯微鏡及HRTEM 高分辨穿透式電子顯微鏡進行分析及研究其微觀組織結構外，另亦針對熱電複合材料塊材進行席貝克係數、電傳導率、熱傳導率、ZT 值的檢測及微硬度與壓縮試驗，藉此瞭解此等塊材的熱電與機械性質，詳細評估實驗所得之數據資料後，將可獲知具微米/奈米複合材料結構之γ-Al2O3/Bi0.4Sb1.6Te3 熱電材料塊材的結構與熱電性能的關聯性，同時也可開發出應用高能量球磨及真空熱壓製程製備具高熱電性能之奈米熱電複合材料塊材的最佳化條件。" "Over the past 30 years, alloys based on Bi2Te3 compounds have been extensively studied and optimized for their use as thermoelectric (TE) materials. Recently, numerous attempts have been made to increase the ZT value of Bi2Te3-based TE materials. One effective method is to increase the electrical conductivity as well as reduce the lattice thermal conductivity of TE materials by alloying, doping, or introducing complex crystal structures. By adopting such principals, several Bi2Te3-based powders with various kinds particle were consolidated into bulk shapes by using different consolidation methods. These including: CNTs/Bi0.4Sb1.6Te3, C60/(Bi,Sb)2Te3, BN/Bi0.4Sb1.6Te3, WO3/Bi0.4Sb1.6Te3, and PbTe/(Bi,Sb)2Te3. The results indicate the thermal conductivity of Bi0.4Sb1.6Te3 can be decreased with addition of CNTs and C60 particles, which eventually can lead to the increase of ZT value. In the case of BN/Bi0.4Sb1.6Te3 and WO3/Bi0.4Sb1.6Te3, the thermal conductivity decreases slightly when the volume fraction of BN and WO3 is increased from 0 vol% to 7 vol%. However, ZT decreases because the addition of the BN and WO3 deteriorates the electrical conductivity seriously. For bulk PbTe/(Bi,Sb)2Te3 samples, the improvement of ZT value was also unsucssecful because the addition of PbTe particles cause the Seebeck coefficient decreased dramatically. From the aforementioned results, it is clear that enhancement of ZT value is strongly depend on the optimal addition of second phase particles into Bi2Te3-based alloys. Recently, it is found that with the addition of the 1.0 vol. % γ-Al2O3 particles into n-type Bi2Se0.3Te2.7 thermoelectric alloy, Bi2Se0.3Te2.7 exhibits the highest ZT value of 0.99 at about 400 K, being 35% improvement compared to the monolithic Bi2Se0.3Te2.7 alloy. This result indicated thermoelectric properties of n-type bismuth-antimony-tellurium alloys can be improved with addition of γ-Al2O3 particles. However, literature survey indicates the enhancement of p-type Bi0.4Sb1.6Te3 alloy with addition of γ-Al2O3 particles has never been reported. Therefore, the goal of this proposal is to investigate the feasibility of preparing newγ-Al2O3/Bi0.4Sb1.6Te3 nanocomposites by a combination of mechanical alloying (MA) and vacuum hot pressing (VHP) techniques. The phase transform and the microstructure formation during the MA processes, and the influences of different MA and VHP parameters on TE properties and mechanical properties will be studied. The structure of as-prepared nanocomposite powders and bulk nanocomposites materials will be examined by XRD, SEM, and TEM. In addition, the measurement of thermal conductivity, Seebeck coefficient and electrical conductivity as well as hardness tests on the bulk nanocomposites materials also will be conducted in order to understand the thermoelectric and mechanical property of the resultant γ-Al2O3/Bi0.4Sb1.6Te3 bulk nanocomposite materials. After comprehensive evaluation of all the experimental results obtained in this work, the influence of the microstructure on the thermoelectric property can be elucidated. The optimum conditions for the production of high thermoelectric performance bulkγ-Al2O3/Bi0.4Sb1.6Te3 nanocomposite through ball milling and vacuum hot pressing routes also can be established."

Keyword(s)

熱電奈米複合材料塊材
熱電優值
氧化鋁粉末
高能量球磨
真空熱壓
Bulk nanocomposite thermoelectric materials
Figure of merit
γ-Al2O3 powder
High energy ball milling
Vacuum hot pressing

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Thermoelectric Properties of Γ-Al2o3 Doped Bi-Sb-Te Materials

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