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Analysis Of Transport Properties of Mechanically Alloyed Lead Tin Telluride.

機譯：機械合金化碲化錫鉛的傳輸性能分析。

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The work described in this thesis had two objectives. The first objective was to develop a physically based computational model that could be used to predict the electronic conductivity, Seebeck coefficient, and thermal conductivity of Pb1-xSnxTe alloys over the 400 K to 700 K temperature as a function of Sn content and doping level. The second objective was to determine how the secondary phase inclusions observed in Pb1-xSn xTe alloys made by consolidating mechanically alloyed elemental powders impact the ability of the material to harvest waste heat and generate electricity in the 400 K to 700 K temperature range.;The motivation for this work was that though the promise of this alloy as an unusually efficient thermoelectric power generator material in the 400 K to 700 K range had been demonstrated in the literature, methods to reproducibly control and subsequently optimize the materials thermoelectric figure of merit remain elusive. Mechanical alloying, though not typically used to fabricate these alloys, is a potential method for cost-effectively engineering these properties. Given that there are deviations from crystalline perfection in mechanically alloyed material such as secondary phase inclusions, the question arises as to whether these defects are detrimental to thermoelectric function or alternatively, whether they enhance thermoelectric function of the alloy.;The hypothesis formed at the onset of this work was that the small secondary phase SnO2inclusions observed to be present in the mechanically alloyed Pb1-xSnxTe would increase the thermoelectric figure of merit of the material over the temperature range of interest. It was proposed that the increase in the figure of merit would arise because the inclusions in the material would not reduce the electrical conductivity to as great an extent as the thermal conductivity. If this were to be true, then the experimentally measured electronic conductivity in mechanically alloyed Pb1-xSnxTe alloys that have these inclusions would not be less than that expected in alloys without these inclusions while the portion of the thermal conductivity that is not due to charge carriers (the lattice thermal conductivity) would be less than what would be expected from alloys that do not have these inclusions. Furthermore, it would be possible to approximate the observed changes in the electrical and thermal transport properties using existing physical models for the scattering of electrons and phonons by small inclusions.;The approach taken to investigate this hypothesis was to first experimentally characterize the mobile carrier concentration at room temperature along with the extent and type of secondary phase inclusions present in a series of three mechanically alloyed Pb1-xSnxTe alloys with different Sn content. Second, the physically based computational model was developed. This model was used to determine what the electronic conductivity, Seebeck coefficient, total thermal conductivity, and the portion of the thermal conductivity not due to mobile charge carriers would be in these particular Pb1-x SnxTe alloys if there were to be no secondary phase inclusions. Third, the electronic conductivity, Seebeck coecient and total thermal conductivity was experimentally measured for these three alloys with inclusions present at elevated temperatures. The model predictions for electrical conductivity and Seebeck coefficient were directly compared to the experimental elevated temperature electrical transport measurements. The computational model was then used to extract the lattice thermal conductivity from the experimentally measured total thermal conductivity. This lattice thermal conductivity was then compared to what would be expected from the alloys in the absence of secondary phase inclusions.;Secondary phase inclusions were determined by X-ray diraction analysis to be present in all three alloys to a varying extent. The inclusions were found not to significantly degrade electrical conductivity at temperatures above 400 K in these alloys, though they do dramatically impact electronic mobility at room temperature. It is shown that, at temperatures above 400 K, electrons are scattered predominantly by optical and acoustical phonons rather than by an alloy scattering mechanism or the inclusions. The experimental electrical conductivity and Seebeck coefficient data at elevated temperatures were found to be within 10 % of what would be expected for material without inclusions. The inclusions were not found to reduce the lattice thermal conductivity at elevated temperatures. The experimentally measured thermal conductivity data was found to be consistent with the lattice thermal conductivity that would arise due to two scattering processes: Phonon-phonon scattering (Umklapp scattering) and the scattering of phonons by the disorder induced by the formation of a PbTe-SnTe solid solution (alloy scattering). (Abstract shortened by UMI.)
機譯：本文所描述的工作有兩個目標。第一個目標是建立一個基于物理的計算模型，該模型可用于預測在400 K至700 K溫度下Pb1-xSnxTe合金的電導率，塞貝克系數(shù)和熱導率隨Sn含量和摻雜水平的變化。第二個目標是確定在固結機械合金化的元素粉末后制得的Pb1-xSn xTe合金中觀察到的第二相夾雜物如何影響材料收集廢熱并在400 K至700 K溫度范圍內發(fā)電的能力。進行這項工作的動機是，盡管在文獻中已經證明了這種合金作為400 K至700 K范圍內異常有效的熱電發(fā)電材料的前景，但是可重復控制并隨后優(yōu)化材料熱電性能的方法仍然難以捉摸。機械合金化雖然通常不用于制造這些合金，但卻是經濟有效地設計這些特性的潛在方法。鑒于機械合金化材料（例如第二相夾雜物）中的晶體完善性存在偏差，因此產生了以下問題：這些缺陷是否對熱電功能有害，或者是否會增強合金的熱電功能。這項工作的結果是，觀察到在機械合金化的Pb1-xSnxTe中存在小的次級相SnO2夾雜物會在目標溫度范圍內提高材料的熱電性能。提出了提高品質因數(shù)的原因，因為材料中的夾雜物不會將導電率降低到與導熱率一樣大的程度。如果這是真的，那么在實驗中測得的含有這些夾雜物的機械合金化Pb1-xSnxTe合金中的電子電導率將不低于不含這些夾雜物的合金中的預期電導率，而部分不是由載流子引起的導熱率（晶格熱導率）將小于沒有這些夾雜物的合金的預期值。此外，有可能使用現(xiàn)有的物理模型來估計電子和聲子通過小夾雜物的散射而觀察到的電學和熱學傳輸性質的變化。;研究該假設的方法是首先通過實驗表征移動載流子濃度在室溫下，以及一系列由三種不同Sn含量的機械合金化Pb1-xSnxTe合金組成的一系列次生夾雜物的范圍和類型。其次，開發(fā)了基于物理的計算模型。如果沒有第二相夾雜物，則使用該模型確定在這些特定的Pb1-x SnxTe合金中，什么是電導率，塞貝克系數(shù)，總熱導率以及不是由移動電荷載流子引起的熱導率部分？ 。第三，通過實驗測量了這三種合金的電子電導率，塞貝克系數(shù)和總熱導率，且夾雜物在高溫下存在。將電導率和塞貝克系數(shù)的模型預測直接與實驗性高溫電傳輸測量值進行比較。然后使用計算模型從實驗測量的總熱導率中提取晶格熱導率。然后將該晶格熱導率與在不存在第二相夾雜物的情況下合金的期望值進行比較。通過X射線衍射分析確定在所有三種合金中均存在不同程度的第二相夾雜物。盡管這些夾雜物對室溫下的電子遷移率有顯著影響，但發(fā)現(xiàn)它們在這些合金中并不會顯著降低其在400 K以上溫度下的導電性。結果表明，在高于400 K的溫度下，電子主要通過光學和聲學聲子散射，而不是通過合金散射機制或夾雜物散射。發(fā)現(xiàn)在升高的溫度下的實驗電導率和塞貝克系數(shù)數(shù)據(jù)在不含夾雜物的材料的預期值的10％以內。未發(fā)現(xiàn)夾雜物在升高的溫度下降低了晶格熱導率。發(fā)現(xiàn)實驗測量的熱導率數(shù)據(jù)與由于兩種散射過程而產生的晶格熱導率一致：聲子-聲子散射（Umklapp散射）和由于PbTe-SnTe的形成引起的無序聲子的散射。固溶體（合金散射）。 （摘要由UMI縮短。）

著錄項

  • 作者

    Krishna, Rajalakshmi.;

  • 作者單位

    Michigan Technological University.;

  • 授予單位 Michigan Technological University.;
  • 學科 Engineering Materials Science.
  • 學位 Ph.D.
  • 年度 2010
  • 頁碼 110 p.
  • 總頁數(shù) 110
  • 原文格式 PDF
  • 正文語種 eng
  • 中圖分類
  • 關鍵詞

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