本文關(guān)鍵詞：熱電轉(zhuǎn)換過程中基于缺陷工程的電聲結(jié)構(gòu)與電熱輸運(yùn)行為調(diào)控　出處：《中國科學(xué)技術(shù)大學(xué)》2017年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 熱電轉(zhuǎn)換 缺陷工程 電子結(jié)構(gòu) 聲子結(jié)構(gòu) 電熱輸運(yùn) 協(xié)同調(diào)控

【摘要】：在無機(jī)功能固體中,電子和聲子同時存在且彼此之間存在固有的耦合關(guān)系,共同決定其本征的物化特性,并使其表現(xiàn)出諸多新奇的物理現(xiàn)象和多樣化的應(yīng)用屬性。因此,對無機(jī)固體中的電子、聲子結(jié)構(gòu)與輸運(yùn)行為進(jìn)行的研究既能實現(xiàn)其本征物化性能的靈活調(diào)節(jié),又為新奇物化現(xiàn)象的探索和新型功能材料(例如熱電效應(yīng)和熱電材料)的設(shè)計指引了方向。熱電材料因能夠直接實現(xiàn)熱能和電能的相互轉(zhuǎn)換,是近年來能源轉(zhuǎn)換材料領(lǐng)域的研究熱點(diǎn)。然而熱電三參數(shù)之間的反比耦合使得熱電材料的ZT值及熱電器件的能量轉(zhuǎn)換效率一直徘徊在較低的水平,嚴(yán)重制約了熱電科技的發(fā)展。理論分析表明熱電性能本質(zhì)上由材料的電子、聲子結(jié)構(gòu)及其輸運(yùn)行為共同決定,且二者常常以晶體中無處不在的晶格缺陷為媒介發(fā)生耦合作用;另一方面,晶格缺陷所對應(yīng)的晶格周期性的破壞也必然會對材料的電子、聲子結(jié)構(gòu)及電、熱輸運(yùn)行為產(chǎn)生影響。上述事實表明在熱電轉(zhuǎn)換過程中有望利用晶格缺陷對電子、聲子結(jié)構(gòu)和電、熱輸運(yùn)行為進(jìn)行調(diào)控,進(jìn)而實現(xiàn)熱電性能的優(yōu)化。本論文工作基于缺陷工程思想,通過向目標(biāo)熱電材料體系中引入特定的晶格缺陷(置換原子、空位等),探究缺陷對體系電子、聲子結(jié)構(gòu)及電、熱輸運(yùn)行為的影響,并在此基礎(chǔ)調(diào)控和優(yōu)化體系的熱電性能。同時,作者結(jié)合缺陷表征和理論計算分析了缺陷調(diào)控的內(nèi)在機(jī)理,發(fā)展了超晶格層間電荷轉(zhuǎn)移等調(diào)控策略,建立了基于缺陷工程的"缺陷結(jié)構(gòu)—熱電性能"構(gòu)效關(guān)系。文末,作者基于自己對缺陷工程策略的理解,重新審視了缺陷調(diào)控自由度的問題,提出了一種基于缺陷工程的"多自由度"協(xié)同調(diào)控的研究思想。論文的主要內(nèi)容包括以下幾個方面:1、本章中,作者選取BiCuSeO天然超晶格熱電材料為研究對象,通過等價離子摻雜的方式在不損害電學(xué)輸運(yùn)性能(即熱電功率因子,PF)的前提下顯著降低了材料的晶格熱導(dǎo)率及總熱導(dǎo)率,從而優(yōu)化其熱電性能。借助于BiCuSeO復(fù)合化合物獨(dú)特的層狀結(jié)構(gòu)([Bi_2O_2]~(2+)絕緣層和[Cu_2Se_2]~(2-)導(dǎo)電層交替堆疊的超晶格結(jié)構(gòu)),通過La、Ag單獨(dú)摻雜和共摻雜兩種摻雜方式置換相應(yīng)層中的Bi、Cu離子,得到等價離子摻雜樣品。電熱輸運(yùn)性能測試表明:由于潛在的能帶收斂效應(yīng),La-Ag共摻雜樣品在提高載流子濃度的同時保持較高的載流子遷移率和Seebeck系數(shù),因而獲得了優(yōu)化的PF,同時借助于摻雜原子的聲子散射效應(yīng),體系的熱導(dǎo)率進(jìn)一步降低,最終使ZT值得到了優(yōu)化。在三種摻雜樣品中,La-Ag共摻雜的效果優(yōu)于單獨(dú)摻雜的樣品,其在755 K時ZT值約為0.46,相對于純樣提高了近70%。該項工作表明等價離子雙摻雜策略能夠同步改善BiCuSeO超晶格材料的熱電性能,同時這種亞層交替堆疊的特殊結(jié)構(gòu)也為在同一物質(zhì)中實施異層雙(多)缺陷協(xié)同調(diào)控研究提供了理想的實驗平臺。2、在上一章工作中,由于使用等價離子摻雜,電導(dǎo)率提升效果受限,功率因子整體偏低。針對這一問題,本章中,作者提出使用空位缺陷來優(yōu)化其電熱輸運(yùn)性能,同時針對傳統(tǒng)的單空位缺陷中可能損害電學(xué)性能的弊端,作者設(shè)計制備了新型的雙空位類型缺陷,通過在合成中同時引入Bi、Cu雙空位首次在BiCuSeO基熱電材料中實現(xiàn)電、熱輸運(yùn)性質(zhì)的協(xié)同優(yōu)化。結(jié)果表明基于空位點(diǎn)缺陷、超晶格界面以及晶界等分級結(jié)構(gòu)的"全尺度"聲子散射可以最大幅度降低系統(tǒng)的熱導(dǎo)率,使雙空位樣品在在750 K得到0.37 Wm-1K-1的極低熱導(dǎo)率。與此同時,正電子湮沒譜測試表明在Bi-Cu雙空位樣品中,空穴電荷有從Bi空位([Bi_2O_2]~(2+)絕緣層)向Cu空位([Cu_2Se_2]~(2-)導(dǎo)電層)轉(zhuǎn)移的趨勢,可以顯著提高Bi_(0.975)Cu_(0.975)SeO樣品中空穴載流子的濃度,增強(qiáng)其電學(xué)輸運(yùn)性能,并最終在750 K時得到0.84的高ZT值,相比于純樣和單空位樣品均有顯著的改善。該項工作表明由Bi-Cu雙空位引發(fā)的層間電荷轉(zhuǎn)移以及基于超晶格結(jié)構(gòu)的全尺度聲子散射能夠協(xié)同調(diào)控BiCuSeO基熱電材料的電學(xué)和熱學(xué)輸運(yùn)性質(zhì),大幅度優(yōu)化其熱電性能。同時這種異層雙空位協(xié)同調(diào)控的實驗策略也為設(shè)計制備高性能的熱電材料提供了新的思路。3、通過簡單固相反應(yīng)合成了 Cu_2ZnSnSe_4純相和空位摻雜樣品。分析結(jié)果表明樣品中含有本征的Se空位和體缺陷,導(dǎo)致Cu、Zn和Sn空位引入后主要以缺陷簇的形式存在,且空位的引入可以造成無序晶疇的產(chǎn)生,引起樣品的部分多晶化。電熱輸運(yùn)性能測試結(jié)果表明空位的引入提高了材料的載流子濃度,進(jìn)而提高了電導(dǎo)率;同時基于空位缺陷簇和晶體孔洞的強(qiáng)烈聲子散射作用以及無序晶疇引起的多晶化,使材料的晶格熱導(dǎo)率和總熱導(dǎo)率均有所降低,從而實現(xiàn)了對材料電導(dǎo)率和熱導(dǎo)率的同步優(yōu)化,并克服了 Seebeck系數(shù)下降的影響,使得空位樣品的ZT值與原始樣相比均有了明顯提升。例如Sn空位樣品Cu_2ZnSn_(0.98)Se_4的ZT值在750 K時達(dá)到了 0.44,是同溫度下原始樣性能的3倍。由于此類物質(zhì)組成元素豐度高且不含污染、高毒的重金屬元素,本章的研究為尋求經(jīng)濟(jì)、低毒的高效熱電材料開辟了新的探索方向。
[Abstract]:In inorganic solids, and the coupling relationship between inherent and between electrons and phonons, determined their intrinsic physicochemical properties, which show many novel physical phenomena and diverse applications of electronic properties. Therefore, inorganic solid in the study of phonon structure and transport behavior which can not only realize the intrinsic physicochemical properties of the flexible adjustment, but also to explore novel physicochemical phenomena and new functional materials (such as thermoelectric effect and thermoelectric materials) direction. The design of thermoelectric materials due to direct conversion of thermal energy and electric energy, energy conversion material is a hot research field in recent years. However the inverse coupling between three parameters makes the thermoelectric energy conversion efficiency of thermoelectric materials ZT and thermoelectric devices has been hovering at a low level, which seriously restrict the development of thermoelectric technology. Theoretical analysis table The thermoelectric properties of materials consisting essentially of electronic structure and phonon transport behavior, joint decisions, and the two often to lattice defects in crystals everywhere as medium coupling; on the other hand, the corresponding lattice defect lattice periodic damage is bound to electronic materials, the phonon structure and electrical. The heat transport effect. The fact that the thermoelectric conversion process is expected to be used in lattice defects on electronic structure and phonon, electricity, heat transport regulation, so as to realize the optimization of the thermoelectric properties. This thesis based on defect engineering ideas, through the introduction of lattice defects specific to the target system (atomic replacement of thermoelectric materials the vacancy, etc.), explore the defects of the system of electronic and electrical, phonon structure, thermal transport behavior, and thermoelectric properties based control and optimization system. At the same time, as a combination of defect characterization And theoretical analysis of inherent mechanism of defect control, the development of super lattice interlayer charge transfer control strategy, based on the project "the defect structure defects of thermoelectric properties" structure-activity relationship. At the end of this paper, author's own understanding of defect engineering based on the strategy, review the defects of regulation of degrees of freedom. This paper proposes a collaborative defect control project "multi degree of freedom based on" research ideas. The main contents of this paper include the following aspects: 1. In this chapter, the author chooses BiCuSeO natural superlattice thermoelectric materials as the research object, through the equivalent ion doping way without damaging the electrical transport properties (thermoelectric power factor PF), under the premise of significantly reduced material total lattice thermal conductivity and thermal conductivity, thereby optimizing the thermoelectric properties. Based on the layered structure of BiCuSeO composite unique compounds ([Bi_2O_2]~ (2 +) insulation layer and [Cu_2Se_2] ~ (2-) superlattice structure alternately stacked conductive layer), through La, Ag single doped and Co doped replacement two doping layer in the corresponding Bi, Cu ion, equivalent ion doped samples. The electric transport performance tests show that the convergence effect due to band potential, La-Ag Co doped samples in improving the carrier concentration while maintaining high carrier mobility and Seebeck coefficient, and the optimization of the PF, and by the phonon scattering effect of dopant atoms, the thermal conductivity of the system is further reduced, making the ZT is optimized. In three kinds of doped samples, effect is better than that of La-Ag doped Co doped samples ZT, its value is about 0.46 at 755 K, compared with the pure sample increased by nearly 70%. of the work showed that the equivalent ion doped strategy can improve BiCuSeO synchronous thermoelectric properties of superlattice materials, and the sub layer are alternately stacked special The structure also is in the same material in the implementation of ISO layer double (multiple) defect cooperative regulation research provides an ideal experimental platform.2, in the last section, due to the use of the equivalent ion doping, the conductivity enhancement effect is limited, the power factor is low. To solve this problem, in this chapter, the author puts forward the vacancy defects to optimize the electric transport properties at the same time, aiming at the drawbacks of single vacancy defects may damage the electrical properties of traditional double vacancy type defects produce a new design for the author, through the synthesis and introduced Bi, Cu for the first time in the electrical double vacancy of BiCuSeO based thermoelectric materials, the collaborative optimization of thermal transport properties. The results show that the vacancy defect based on Superlattice interface and grain boundary classification structure of the "full scale" can greatly reduce the phonon scattering system of thermal conductivity, the double vacancy in 750 samples in K to 0.37 Wm-1K-1 very low Thermal conductivity. At the same time, the positron annihilation spectra show that in Bi-Cu double vacancy samples, hole charge from Bi vacancies ([Bi_2O_2]~ (2+) insulation layer) to the Cu vacancy ([Cu_2Se_2]~ (2-) conductive layer) transfer, can significantly improve the Bi_ (0.975) Cu_ (0.975) SeO samples of the hole carrier concentration and enhance the electrical transport properties, and finally get the high ZT value of 0.84 at 750 K, significant improvements compared to the pure samples and samples have a single vacancy. This work showed that the charge transfer caused by Bi-Cu double vacancy layer and between full scale phonon scattering superlattice structure based on synergistic regulation of BiCuSeO based thermoelectric the material of the electrical and thermal transport properties, greatly optimize the thermoelectric properties. At the same time, the experimental strategy of different layers of divacancies coordinated regulation also provides new ideas for the design and preparation of.3 thermoelectric materials with high performance, through a simple solid state reaction The pure and Cu_2ZnSnSe_4 vacancy doping samples. Analysis results show that samples containing Se vacancies and defects, the intrinsic cause Cu, Zn and Sn after the introduction of the main vacancy defect clusters to form, and the introduction of vacancies can cause disordered crystalline has caused some more crystallization samples. The thermoelectric transport properties test the results show that the vacancy was improved by the introduction of the carrier concentration in the material, thus improving the conductivity and crystallization; strong phonon scattering effect of vacancy defect clusters and crystal holes and disordered crystal domain caused by the material based on the lattice thermal conductivity and thermal conductivity decreased, so as to achieve simultaneous optimization of material conductivity and thermal conductivity, and to overcome the effect of Seebeck coefficient decreased, the vacancy of ZT value of the sample and original sample has improved significantly. For example, Sn Cu_2ZnSn_ (0.98) Se_4 vacancy samples at ZT value of 7 At 50 K, it reached 0.44, which is 3 times higher than that of the original sample at the same temperature. Due to the high abundance and no pollution of such substances, the research of this chapter opens up a new direction for searching for economical, low toxic and high efficiency thermoelectric materials.

【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：TB303

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