本文選題：熱電材料 + MgAgSb合金��； 參考：《哈爾濱工業(yè)大學》2017年博士論文

【摘要】：MgAgSb合金在300~548K溫度區(qū)間具有較低的本征熱導率,但載流子濃度較低,尚未達到最佳范圍,功率因子和熱電優(yōu)值仍有較大提升空間。此外,該合金的電熱輸運機制尚不清楚,制約進一步的性能優(yōu)化。本文主要通過元素摻雜增大MgAgSb基合金的載流子濃度,提高功率因子和熱電優(yōu)值。利用X射線衍射儀、透射電子顯微鏡、Seebeck系數(shù)/電導率綜合測試系統(tǒng)、閃光導熱儀和綜合物性測量系統(tǒng)等手段主要研究了燒結(jié)溫度、合金成分和Mg位摻雜(Li、Ca和Yb)對MgAgSb基合金的微觀組織、輸運特性和熱電性能的影響規(guī)律,采用單能帶拋物線理論結(jié)合聲學支散射模型和Debye-Callaway模型及結(jié)構(gòu)分析查明電熱輸運機制,揭示摻雜改性機理。研究發(fā)現(xiàn),燒結(jié)溫度對MgAg_(0.97)Sb_(0.99)合金的晶粒尺寸、相組成和熱電性能有明顯影響。當燒結(jié)溫度不高于573K時,MgAg_(0.97)Sb_(0.99)合金為純相,晶粒尺寸較小(約150nm);當燒結(jié)溫度為593K時,晶粒尺寸顯著增大(1~5μm);當燒結(jié)溫度為613K時,出現(xiàn)微量第二相。隨燒結(jié)溫度升高,載流子濃度先降低后上升,功率因子先減小后增大,總熱導率單調(diào)增大,熱電優(yōu)值下降。通過優(yōu)選合金成分,即增加Sb含量,增大了MgAg_(0.97)Sb_(0.99+x)合金的載流子濃度,提高了功率因子。當x不高于0.005時,合金為純相;當x為0.01時出現(xiàn)Sb納米顆粒。Sb含量增加,載流子濃度與電導率先顯著增大后略減小,功率因子單調(diào)升高,其中室溫值由18.2μWcm-1K-2升至22.9μWcm-1K-2。同時總熱導率也增大,熱電優(yōu)值未見提高,但高功率因子有利于提高熱電器件的輸出功率密度。采用理論模型計算確定MgAg_(0.97)Sb_(0.99)合金的最高功率因子對應(yīng)的最佳載流子濃度為9.0×1019cm-3,未摻雜合金的載流子濃度僅為2.7×1019cm-3,通過Li摻雜大幅度增大Mg1-xLixAg_(0.97)Sb_(0.99)合金的載流子濃度,顯著提高功率因子。隨Li摻雜量增加,功率因子先升高后降低,當x=0.01時出現(xiàn)峰值,室溫為24.0μWcm-1K-2;同時晶格熱導率先減小后增大,最終平均熱電優(yōu)值(300~548K)略有提高,從1.0(x=0)升至1.1(x=0.01)。采用Ca或Yb摻雜增大Mg_(1-x)M_xAg_(0.97)Sb_(0.99)(M=Ca或Yb)合金的載流子濃度,降低晶格熱導率,提高熱電優(yōu)值。Ca摻雜量增加,Mg1-xCaxAg_(0.97)Sb_(0.99)合金的載流子濃度單調(diào)增大,功率因子升高;產(chǎn)生晶格畸變,降低晶格熱導率。Yb摻雜量增加,Mg1-xYbxAg_(0.97)Sb_(0.99)合金的載流子濃度先升高后基本不變,功率因子先升高后略降低;晶格熱導率先顯著降低后升高,熱電優(yōu)值在x=0.005時達最大,最高熱電優(yōu)值在548K為1.4。相比Ca摻雜,相同量Yb摻雜造成更強烈的晶格畸變,顯著降低晶格熱導率,明顯提高熱電優(yōu)值。采用高能球磨結(jié)合快速燒結(jié)方法制備出納米結(jié)構(gòu)的MgAgSb合金,通過引入高密度的空位晶界、層錯、位錯等缺陷,大幅度增強了聲子散射概率,降低了晶格熱導率。MgAg_(0.97)Sb_(0.99)合金的本征載流子濃度遠低于理論最佳值,主要通過元素摻雜增大載流子濃度,提升功率因子,同時晶格畸變降低晶格熱導率,提高熱電優(yōu)值。
[Abstract]:The MgAgSb alloy has a lower intrinsic thermal conductivity at the temperature range of 300~548K, but the carrier concentration is low, and it has not reached the optimum range. The power factor and the thermoelectric merit still have a larger lifting space. In addition, the electrothermal transport mechanism of the alloy is not yet clear, which restricts the further performance optimization. This paper mainly increases the MgAgSb bonding through the doping of elements. X ray diffractometer, transmission electron microscope, Seebeck coefficient / conductivity comprehensive testing system, flash thermo thermal conductivity meter and comprehensive physical measurement system are used to study the sintering temperature, alloy composition and Mg doping (Li, Ca and Yb) on the microstructure of MgAgSb based alloys. The influence laws of transport characteristics and thermoelectric properties are investigated by using the single energy band parabola theory, the acoustic support scattering model and the Debye-Callaway model and the structural analysis to find out the mechanism of the electric heat transport and reveal the mechanism of doping modification. It is found that the sintering temperature has a significant influence on the grain size, phase composition and thermoelectric properties of MgAg_ (0.97) Sb_ (0.99) alloy. When the sintering temperature is not higher than 573K, the MgAg_ (0.97) Sb_ (0.99) alloy is a pure phase, and the grain size is smaller (about 150nm). When the sintering temperature is 593K, the grain size increases significantly (1~5 m). When the sintering temperature is 613K, the second phase appears. With the sintering temperature rising, the carrier concentration decreases first and then rises, the power factor decreases first and then increases, the total thermal conductivity is increased. The total thermal conductivity is increased. By optimizing the alloy composition, that is, increasing the Sb content, increasing the carrier concentration of MgAg_ (0.97) Sb_ (0.99+x) alloy and increasing the power factor. When x is not higher than 0.005, the alloy is pure phase, and when x is 0.01, the Sb nanoparticles.Sb content increases, and the carrier concentration and electrical conductivity first increase significantly after a significant increase in the carrier concentration and conductivity. The power factor increases monotonously, in which the room temperature rises from 18.2 to 22.9 Wcm-1K-2 to 22.9 Mu and the total thermal conductivity increases, and the thermoelectric merit is not improved, but the high power factor is beneficial to the increase of the output power density of the thermoelectric device. The optimum carrier of the maximum power factor of MgAg_ (0.97) Sb_ (0.99) alloy is determined by theoretical model calculation. The concentration is 9 x 1019cm-3, the carrier concentration of the undoped alloy is only 2.7 x 1019cm-3. The carrier concentration of Mg1-xLixAg_ (0.97) Sb_ (0.99) alloy is greatly increased by Li doping, and the power factor is significantly increased. With the increase of Li doping, the power factor rises first and then decreases, when the X =0.01 is at the peak value and the room temperature is 24 um Wcm-1K-2; and the lattice heat is at the same time. The ultimate average thermoelectric value (300~548K) increases slightly from 1 (x=0) to 1.1 (x=0.01). The carrier concentration of Mg_ (1-x) M_xAg_ (0.97) Sb_ (0.99) (M=Ca or Yb) alloy is increased by Ca or Yb doping, the thermal conductivity of the lattice is reduced, the doping amount of the thermoelectric value increases, and the carrier concentration of the alloy (0.97) (0.99) is increased. With the increase of degree monotonicity and the increase of power factor, lattice distortion and lattice thermal conductivity.Yb doping increase, the carrier concentration of Mg1-xYbxAg_ (0.97) Sb_ (0.99) alloy increases first, and the power factor rises first and then decreases slightly; the thermal conductivity of lattice is the first to decrease, and the thermoelectric value reaches the maximum at x=0.005, and the highest thermoelectric merit is at the highest value. 548K doping with the same amount of Yb leads to more intense lattice distortion of the same amount of Yb, which significantly reduces the thermal conductivity of the lattice and obviously improves the thermoelectric value. The nano structure MgAgSb alloy is prepared by high energy ball milling and rapid sintering. By introducing high density vacancy grain boundary, stacking error, dislocation and other defects, the phonon scattering is greatly enhanced. The intrinsic carrier concentration of.MgAg_ (0.97) Sb_ (0.99) alloy is much lower than that of the theoretical optimum. The carrier concentration increases mainly through the doping of the element, and the power factor is increased. The lattice distortion reduces the thermal conductivity of the lattice and improves the thermoelectric value.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TG146.22

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