The Thermoelectric Properties of BiO.4Sb1.6Te3 Bulk Nanocomposites Fabricated by Powder Metallurgy

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Project title

Code/計畫編號

MOST103-2221-E019-013

Translated Name/計畫中文名

具非晶/奈米、奈米/奈米、微米/奈米結構Bi0.4Sb1.6Te3複合材料塊材之粉末冶金製程與熱電特性研究

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=8358562

Year

2014

Start date/計畫起

01-08-2014

Expected Completion/計畫迄

31-07-2015

Bugetid/研究經費

1045千元

ResearchField/研究領域

材料科技

"奈米熱電複合材料塊材之研究雖已進行多年，然文獻調查發現，運用球磨和熱壓方式製備出具非晶/奈米複合材料 (Amorphous/Nanocrystal Composite)結構之奈米熱電複合材料塊材的研究至今仍無人進行，非晶質合金是一符合PGEC (phonon-glass/electron-crystal)構想的材料，此乃因非晶質合金為金屬顆粒，故其導電率(σ)將比SiC、Y2O3、BN等非金屬化合物高，此預期可提高功率因子α2σ(α:席貝克係數)，而其雜亂無序的原子結構亦會對聲子的運動產生強烈的散射現象進而降低熱傳導率(κ)，故此種添加非晶質合金顆粒形成之非晶/奈米複合材料結構之奈米熱電複合材料塊材可望會因添加非晶質合金顆粒而提高其熱電優值(ZT，ZT=α2σT/κ，T:絕對溫度)。又最近利用過濾效應思維來合成具奈米/微米結構的熱電複合材料也成為熱電材料的重要研究方向。在奈米/微米結構的熱電複合材料中，由於奈米相粒子散佈的目的是為了幫助聲子的散射，而微米級顆粒則形成電子傳輸的網絡，因此根據過濾效應所形成的奈米/微米結構在一定程度上可改變熱電複合材料中熱和電傳導的互動關係，進而提高熱電材料性能。因此本研究先以高能量球磨機將非晶Ti50Cu28Ni15Sn7、奈米Ti50Cu28Ni15Sn7、奈米Bi0.4Sb1.6Te3、微米Bi0.4Sb1.6Te3 等四種粉末依設定比例以高能量球磨機合成具非晶/奈米、奈米/奈米、微米/奈米等結構之Bi0.4Sb1.6Te3熱電複合材料粉末後，再利用真空熱壓成型技術將此熱電複合材料粉末製備成塊材，由於研究範圍頗廣，一年內無法完成所有的實驗工作，故本計畫將以二年的時間進行，第一年先進行具非晶/奈米與奈米/奈米結構之Bi0.4Sb1.6Te3熱電複合材料製備工作。第二年之工作重點則在具微米/奈米結構之Bi0.4Sb1.6Te3熱電複合材料的製造，所配製之熱電複合材料粉末與塊材，除將依序以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，藉此瞭解具非晶/微米/奈米等結構之Bi0.4Sb1.6Te3熱電複合材料塊材的熱電性質；詳細評估所得之數據資料後，除可獲知具非晶/微米/奈米等結構之Bi0.4Sb1.6Te3塊材的材料特性與熱電性能的關聯性外，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具非晶/微米 /奈米等結構之Bi0.4Sb1.6Te3奈米熱電複合材料塊材的最佳化條件。" "Of the various types of bulk nanostructured thermoelectric materials, the nanocomposite type bulk materials have shown the most promise for commercial use because, unlike many other type nanostructured materials, its ZT values can be increased by reducing the thermal conductivity while allowing for large scale, quick, and inexpensive fabrication. To further decrease the thermal conductivity, additional phases have been dispersed into the nanocomposite thermoelectric materials. It is postulated that the addition of second-phase nanoparticles will work as phonon scattering centers and further decrease thermal conductivity. Among the various types of additional phases, metallic amorphous materials fulfill the criterion of PGEC. It is suggested that the addition of amorphous particles into the thermoelectric materials can contribute to the decrease in thermal conductivity and raise the electric conductivity, both effects finally can yield the increase of ZT values. However, a detailed literature survey indicates the enhancements in thermoelectric properties by this approach have never been reported. Recently, a percolation effect has been introduced to tune thermoelectric transport properties. According to the principle of the percolation effect, the electron charge carriers likely ‘select’ a path — the low-resistivity channel connected by the large grains — whereas the phonons do not choose their path. The system of channels via coarse grains would have low electrical resistivity and thermal conductivity if more fine particles are included. As the Seebeck coefficient does not change significantly by varying the grain size, the ZT value could be tuned by adjusting the volume percentage of fine particles. Therefore, it is necessary to initiate a proposal to study the validity of above concepts which has never been discussed. Consequently, the purpose of present work is to investigate the feasibility of preparing new nanocomposites by a combination of ball milling and vacuum hot-pressing techniques. The whole program will be carried out in two years after careful consideration of huge experimental works. The main goal in the first year is the preparation of amorphous-Ti50Cu28Ni15Sn7/nano-Bi0.4Sb1.6Te3 and nano-Ti50Cu28Ni15Sn7/nano-Bi0.4Sb1.6Te3 nanocomposites. The experimental work in the second year will be focused on the fabrication of micro-/nano-Bi0.4Sb1.6Te3 nanocomposite by employing Bi0.4Sb1.6Te3 powders with different particles and grain sizes 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 compression tests on the bulk nanocomposites materials also will be conducted in order to understand the thermoelectric and mechanical property of the resultant 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 bulk nanocomposite through ball milling and vacuum hot pressing routes also can be established."

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The Thermoelectric Properties of BiO.4Sb1.6Te3 Bulk Nanocomposites Fabricated by Powder Metallurgy

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