以工程技術調控SnSe和CaZn2Sb2熱電材料於廢回收之應用;Engineering Tin Chalcogenide and Zintl Phase Thermoelectric Materials for Waste Heat Recovery

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題名:	以工程技術調控SnSe和CaZn2Sb2熱電材料於廢回收之應用;Engineering Tin Chalcogenide and Zintl Phase Thermoelectric Materials for Waste Heat Recovery
作者:	泰士仁;Wubieneh, Tessera Alemneh
貢獻者:	物理學系
關鍵詞:	替代性和永續性能源;熱電效應;alternative and sustainable energy sources;Thermoelectric effect
日期:	2017-05-02
上傳時間:	2017-10-27 13:39:31 (UTC+8)
出版者:	國立中央大學
摘要:	隨著對環境保護和對使用潔淨能源的日益需求與關注，促成了開發替代性和永續性能源的相關研究。熱電效應是一種能將熱能與電能做直接及可逆的轉換，並為廢熱發電提供可行的途徑。熱電材料在發電領域變得越來越重要，在沒有排放有毒物質的情況下實現製冷，為解決當今的能源和環境問題提供了很大的契機。在所有先進的高溫熱電材料中，由於硒化錫和鈣鋅銻礦化合物表現出低熱導率和高熱電優質係數，現已經被確認為極具潛力的熱電材料。硒化錫在室溫下被廣泛認為是一種簡單的層狀正交晶體結構，與氯化鈉結構的三維變形相似。據報導，單晶硒化錫最佳的熱電優質係數值在923 K時約為2.6。然而，單晶製造方法與較差的機械性能，阻礙了該材料在熱電器件的實際應用。因此，找到其多晶對應物並適合工業規模生產出高密度熱電材料是非常迫切需要的。摻雜的方式除了可降低其熱傳導性也能調控材料的載流子濃度，是能最有效優化p型硒化錫和鈣鋅銻礦化合物的熱電性能。在本論文中，我們提出並且成功地藉由熔融、淬火和火花電漿燒結術製備高密度多晶鍺摻雜硒化錫和銪摻雜鈣鋅銻礦化合物塊材，以達到改質樣品的熱電與機械性能。在這項研究中，p型多晶鍺摻雜硒化錫系統中的錫可被鍺所取代，近而調控材料的傳輸性質。我們發現鍺摻雜雖可產生晶格缺陷，但卻能增加材料的西貝克係數，同時也可藉由增強聲子散射，以達到降低晶格熱導率。所有鍺取代的樣品都顯示出低導熱性，這主要歸因於來自無序摻雜原子的聲子散射和硒化錫結構中原子鍵結的產生的顯著非諧調性質。因此，在800 K時，1% 的鍺摻雜硒化錫便可達到最高的熱電優質係數0.77。該數值比未摻雜的多晶硒化錫（zT = 0.56）增強了約40 ％。同樣地，Zintl相這類的材料也是可以用於熱電器件的另一種材料。因為這類材料具備理想熱電材料（西貝克係數、電阻率、導熱性）該有的複雜晶體結構。在Zintl相中，p型多晶銪摻雜鈣鋅銻礦化合物中利用銪取代鈣原子位置，以達到優化傳輸性能。當銪原子取代鈣原子後，由於載流子濃度提高和熱傳導降低，導致材料的電阻率降低了約50 ％以上。這是由於藉由在晶格中陽離子位置引入多個離子所導致的結構無序，進而使得聲子的散射提高。因此，稀土元素銪在鈣陽離子位置的取代顯著地增加了熱電優質係數。研究結果證實，利用鍺和銪摻雜都能是可有效提高硒化錫和鈣鋅銻礦等化合物的熱電性能。;With increasing concerns regarding environmental protection and the growing demand to use clean energy have stimulated research to develop an alternative and sustainable energy sources. Thermoelectric effect enables direct and reversible conversion of thermal energy into electrical energy, and provides a viable route for power generation from waste heat. Thermoelectric (TE) materials are becoming increasingly important in the field of electricity generation and realize refrigeration without the emission of toxic matters, offer a great opportunity for solving today’s energy and environmental issues. Among all state-of-the-art high temperature thermoelectric materials, SnSe and CaZn2Sb2 have been firmly established as a potential TE material, which exhibit low thermal conductivity and high figure of merit values. SnSe widely identified as a simple layered orthorhombic crystal structure at room temperature, which is similar with a three dimensional distortion of NaCl structure. It has been reported that a single crystal SnSe shows excellent thermoelectric performance, with zT value around 2.6 at 923 K. The single crystal fabrication method and the poor mechanical property, which prevent the practical applications of thermoelectric devices. Therefore, it is quit essential to find its polycrystalline counterparts to fabricate highly dense thermoelectric materials and suitable for an industrial scale up. Doping is an effective way to optimize the thermoelectric properties of p-type SnSe and CaZn2Sb2 by reducing its thermal conductivity and adjusting its carrier concentration. In this dissertation, it is proposed that highly dense polycrystalline (Sn1-xGex)Se and (Ca1-xEux)Zn2Sb2 bulks could be prepared by melt-quench and spark plasma sintering method to engineer the thermoelectric performance and mechanical properties of specimens. We successfully fabricated highly dense pure polycrystalline (Sn1-xGex)Se and (Ca1-xEux)Zn2Sb2 bulk samples using the proposed melt-quench and spark plasma sintering approach. In this study, Sn was substituted with Ge in the p-type polycrystalline (Sn1-xGex)Se system to engineer the transport property. We found that Ge doping increases Seebeck coefficient and simultaneously reduces lattice thermal conductivity by enhancing phonon scattering via lattice defect. All germanium substituted samples show low thermal conductivity, which is mainly attributed to phonon scattering from disordered dopant atoms and the high anharmonic boding nature of SnSe. As a result the highest TE dimensionless figure of merit zT = 0.77 was obtained for (Sn0.99Ge0.01)Se at 800 K, which shows 40% enhancement over the pristine polycrystalline SnSe (zT=0.56). Similarly, Zintl phases are a class of materials that can be used in TE devices because they often possess complex crystal structures necessary for the desired thermoelectric properties (Seebeck, electrical resistivity, thermal conductivity). Ca was substituted with Eu in the Zintl phase p-type polycrystalline (Ca1-xEux)Zn2Sb2 compound to optimize the transport property. After europium substitution it shows that more than 50% decrement in electrical resistivity because of high charge carrier concentration and low thermal conductivity due to high phonon scattering through structural disorder yielded by the incorporation of multiple ions in the cation. Consequently, the cationic substitution of rare earth element Eu in the Ca site significantly increased thermoelectric dimensionless figure of merit. These results indicate that doping with Ge and Eu are an effective approach to enhance thermoelectric performance of SnSe and CaZn2Sb2 compounds respectively.
顯示於類別:	[物理研究所] 博碩士論文

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