High temperature thermoelectric properties of skutterudite-Bi2Te3 nanocomposites

Nanocomposite engineering has been proved effective in diverse regimes of material research to attain a performance beyond each constituent phase. In this work, Yb-filled CoSb₃ (bulk matrix/host)-Bi_0.4Sb_1.6Te₃ (secondary inclusion) thermoelectric nanocomposites have been synthesized via an ex situ process. Bi_0.4Sb_1.6Te₃ inclusions are mainly distributed at the grain boundaries of Yb_0.2Co₄Sb₁₂ matrix in the composites. In particular, Te diffuses in situ from Bi_0.4Sb_1.6Te₃ through Yb_0.2Co₄Sb₁₂ matrix during the hot pressing process. This, combined with the grain boundary effect, results in favorable changes in the carrier concentration, carrier mobility, electrical resistivity, Seebeck coefficient, and thermal conductivity. Such synergistic changes are notably absent in the stand-alone Te-doped Yb-filled CoSb₃, suggesting the key role of diffusion and grain boundaries. As a result, a maximum ZT value of 0.96 has been attained for Yb_0.2Co₄Sb₁₂-2 wt% Bi_0.4Sb_1.6Te₃ at 650 K. The present work opens a new avenue towards high performance thermoelectric composites via controlled inter-constituent diffusion and grain boundary effect.     

Synthesis and thermoelectric properties of CoSb3/WO3 thermoelectric composites

In this study, nano-sized WO₃ powder was dispersed into CoSb₃ powder by ball milling and CoSb₃/WO₃ thermoelectric composites were fabricated using hot-pressing sintering. The results showed that the WO₃ phase distributed uniformly in the form of clusters and the average size of cluster was lower than 4 μm. As the content of WO₃ increased, the electrical conductivity and Seebeck coefficient of CoSb₃/WO₃ composites decreased. The thermal conductivity of composites decreased obviously which resulted from the phonon scattering by the WO₃ inclusions locating on the grain boundaries of CoSb₃ matrix. The highest thermoelectric figure of merit ZT = 0.40 was achieved at 650 K for CoSb₃/2%WO₃ composite.     

Zr5Si3及Zr3Ti2Si3弹性性质与热学性质

应用基于密度泛函理论的平面波赝势方法计算16H金属硅化物Zr5Si3及Zr3Ti2Si3的基态晶格参数,得出弹性常数、体弹性模量、弹性模量、剪切模量及泊松比等弹性性质.利用弹性常数计算德拜温度、格林奈森常数,并在德拜-格林奈森模型基础上计算这两种金属硅化物的各向异性热膨胀系数,由此得出Zr5Si3的a、c方向各向异性热膨胀系数(高温时)分别为8×10-6和15×10-6,对Zr3Ti2Si3(高温时)分别为11×10-6和13×10-6,与实验基本相符.根据方向体弹性模量、方向弹性模量及重叠布居数讨论两种材料各向异性热膨胀不同的原因.     

硅纳米线复合Mg2Si基热电材料的制备与性能研究

利用溶液法混合粉体并通过电场激活压力辅助烧结(FAPAS)方法制备了不同硅纳米线含量的Mg_2Si基复合热电材料,研究了硅纳米线的掺入及含量对基体材料热电性能的影响。结果表明:硅纳米线掺入后材料电导率大幅降低,塞贝克系数基本不变,热导率小幅降低。随着硅纳米线掺量增加,材料电导率降低,塞贝克系数稍有提高,热导率有升高趋势。硅纳米线掺量为0.1at%的样品在800 K时ZT值达到最高值0.5。     

N型和P型Si80Ge20合金制备及热电性能

对N型Si80Ge20(P4)x及P型Si80Ge20Bx固溶体合金的化学计量比进行了研究,采用已总结出的最佳工艺条件,制备了一系列N型、P型固溶体合金,并比较了各系列样品的热电性能.结果表明,x=1.5的N型Si80Ge20(P4)x固溶体合金具备良好的热电性能,与未掺杂Si80Ge20固溶体合金相比,最高热电优值ZT为0.651,提高了3.34倍.x=1.5的P型Si80Ge20Bx固溶体合金也具备较佳的热电性能,最高热电优值(ZT)值为0.538.     

Crystal structure and thermoelectric properties of β-MoSi2

A powder sample of a metastable phase β-MoSi₂ having the C40-type crystal structure was prepared by heating Mo sheets with a Na–Si melt at 858 K for 12 h to determine details of the crystal structure. The lattice constants (a = 4.6016(3) Å and c = 6.5700(3) Å) and Si atom coordinate (y = 0.1658(2)) of β-MoSi₂ were determined by Rietveld analysis of the X-ray powder diffraction. The thermoelectric properties were refined for a bulk sample prepared by sintering the β-MoSi₂ powder at 773 K and 600 MPa. The electrical resistivity of the sintered β-MoSi₂ sample with a relative density of 65% of the theoretical one was 2.5 mΩ cm at 300 K, and slightly increased with increasing temperature from 300 to 725 K. The Seebeck coefficients changed from +60 to +89 μV/K in the temperature range from 330 to 725 K. The maximum thermoelectric power factor was 2.2 × 10^?6 W cm^?1 K^?2 at 725 K.     

Effect of powder mixing on thermoelectric properties in Bi2Te3-based sintered compounds

The effect of powder mixing on thermoelectric properties was studied in n-type Bi₂Te_2.85Se_0.15 compounds and p-type Bi_0.5Sb_1.5Te₃ compounds. The figure-of-merit of the n- and p-type sintered compounds was strongly affected by carrier mobility. The use of coarse powders (200–300 μm) was beneficial to improve the crystallographic orientation of sintered compound. However, voids in the compound decreased the carrier mobility. As the fine powders (below 45 μm) were blended with coarse powders up to about 30%, the carrier mobility was increased due to the reduction of the voids. The addition of fine powders over 30% degraded the carrier mobility due to the decrease of crystallographic orientation and the increase of particle boundary. When the fine powder content was 20%, the n- and p-type compounds exhibited the maximum figure-of-merit of 2.31 × 10⁻³ K⁻¹ and 2.89 × 10⁻³ K⁻¹, respectively.     

Composition-dependent thermoelectric properties of PbTe doped with Bi2Te3

The composition-dependent thermoelectric properties of PbTe doped with Bi₂Te₃ have been studied at room-temperature. The electrical resistivity and the Seebeck coefficient in absolute value decrease with an increase of Bi₂Te₃. A sharp maximum in the Seebeck coefficient at 0.3 mol% Bi₂Te₃ indicates that an electronic topological transition is occurred in PbTe alloyed with Bi₂Te₃. The total thermal conductivity nearly keeps constant and the parts of lattice, which are much lower than those doped with PbI₂ prepared by hot-pressing, linearly decrease with increasing Bi₂Te₃. The figure of merit shows a maximum value of 7.63 × 10⁻⁴ K⁻¹, which is several times higher than that of PbTe containing other dopants. The high thermoelectric performance is explained by electronic topological transition induced by alloying.     

The electric and thermoelectric properties of CuInSe2-based chalcopyrite

It has been found that CuInSe₂ chalcopyrite is an extrinsic semiconductor that exhibits a more complex temperature dependence of its electric conductivity than conventional extrinsic semiconductors. This temperature dependence of the electric conductivity results from the complex structure of the electron energy spectrum in these crystals. The temperature dependence of the electric conductivity has been used to determine the activation energies of the energy levels of the intrinsic defects that are formed upon the violation of the stoichiometry of the CuInSe₂ structure. The analysis of the temperature dependence of the thermoelectric power has revealed that the main scattering mechanism at high temperatures is acoustic-phonon scattering.     

Fabrication and thermoelectric properties of crystal-aligned nano-structured Bi2Te3

With a view to experimental demonstration for an improved thermoelectric performance, a slip casting method under high magnetic field for uni-directionally aligned crystals has been investigated. The sintered body of Bi₂Te₃ powder, its size between 300 and 500 nm, green-bodied under 6 T magnetic field showed a 33% variation in the fraction of the directionally aligned crystals. According to increasing this fraction, electrical resistivity was reduced with keeping thermal conductivity and Seebeck coefficient unchanged. This could be explained from the fact that the aligned crystals by magnetic field has increased the carrier mobility keeping carrier concentration unchanged.     

Mg_2Si热电材料微波固相合成研究

为了解决传统方法制备Mg2X(X=Si、Ge、Sn)基热电材料过程中带来Mg的氧化,挥发等问题,引进微波低温固相反应法,成功合成了Mg2Si粉体,用XRD分析手段对合成的粉体物相进行了表征,并系统研究了合成工艺对粉体制备的影响。结果表明:通过采用合适的加热工艺制度可以抑制Mg氧化;控制Mg过量可以补偿Mg的挥发;本实验条件下,当Mg过量0.0125mol、加热功率在2.5kW(853K)下保温30min时,可以得到单相Mg2Si热电化合物粉体。     

Synergistically enhanced thermoelectric properties of Bi2S3 bulk materials via Cu interstitial doping and BiCl3 alloying

Bi2S3 is composed of inexpensive and environ-mental friendliness elements,which has received extensive interests and been investigated as a promising mid-temper...     

Rapid synthesis of CoSb3 by MA-SPS and its thermoelectric properties

Bulk CoSb3 with single phase was synthesized by mechanical alloying and spark plasma sintering （MA-SPS）. The thermoelectric properties of bulk CoSb3 prepared by different technologies were investigated. All samples have the character of typical semiconductor electricity and their thermoelectric figures of merit （ZT） get the maximum values at 400℃. The highest ZT value is 0.0571, belonging to the sample sintered at 600℃ among all samples at all temperatures.     

Stoichiometry and mechanical properties of Mo3Si

The A15 phase Mo₃Si is an important constituent of a new class of silicides based on Mo–Si–B. In this research it will be shown that, contrary to published results, single-phase Mo₃Si is slightly off-stoichiometric. In addition, it remains single phase in a small composition range. Its room temperature fracture toughness is on the order of 3 MPa m^1/2. The compressive strength at 1400°C in argon decreases with decreasing strain rate and increasing Si concentration.     

First-principles investigations of structural,mechanical, electronic and optical properties of U3Si2-type AlSc2Si2 under high pressure

The structural, elastic, electronic and optical properties for U₃Si₂-type AlSc₂Si₂ compound under pressure were systematically investigated by using the first-principles calculations. The values of elastic constants and elastic moduli indicate that AlSc₂Si₂ keeps mechanical stability under high pressure. The mechanical properties of AlSc₂Si₂ are compared with those of Al₃Sc. The results indicate that AlSc₂Si₂ is harder than Al₃Sc. Anisotropic constant A^U and 3D curved surface of elastic moduli predict that AlSc₂Si₂ is obviously anisotropic under pressure. The electronic structure of AlSc₂Si₂ exhibits metallic character and the metallicity decreases with the elevated pressure. In addition, optical properties as a function of pressure were calculated and analyzed. The present work provides theoretical support for further experimental work and industrial applications.     

(Al_2O_3+Si)_p/Al系铝基复合材料的原位制备及性能

以Al-Si O2为体系,通过粉末冶金液相烧结的方法原位合成(Al2O3+Si)p/Al系铝基复合材料,利用XRD、DSC和SEM等测试技术测试了复合材料的相组成、密度、电导率及热膨胀性能,观察了Si相和Al2O3相的形貌并分析了相与相之间的反应界面。结果表明,通过该方法可以制备出具有优良性能的电子封装材料,其密度、电导率和热膨胀系数分别达到了2.5 g/cm3、10-7Ω·m和5×10-6/K。原位生成的Al2O3相多数呈圆球状颗粒,Si相以片状形成,随着烧结温度的提高,两种相和基体结合紧密,分布更加均匀分散,且无界面反应物生成。     

Enhanced thermoelectric performance of Bi_2Se_3/TiO_2 composite

Bi₂(Te,Se)₃ alloys are conventional commercial thermoelectric materials for solid-state refrigeration around room temperature.In recent years,much attention has been paid to various advanced thermoelectric composite materials due to the unique thermoelectric properties.In this work,Bi₂Se₃/TiO₂ composites were prepared by hot pressing the plate-like Bi₂Se₃ powders coated in situ with hydrolyzed hytetabutyl-n-butyl titana...     

Thermoelectric properties of Sb-doped Mg2Si semiconductors

The thermoelectric properties of Sb-doped Mg₂Si (Mg₂Si:Sb = 1:x(0.001 ≦ x ≦ 0.02)) fabricated by spark plasma sintering have been characterized by Hall effect measurements at 300 K and by measurements of electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) between 300 and 900 K. Sb-doped Mg₂Si samples are n-type in the measured temperature range. The electron concentration of Sb-doped Mg₂Si at 300 K ranges from 2.2 × 10¹⁹ for the Sb concentration, where x = 0.001, to 1.5 × 10²⁰ cm⁻³ for x = 0.02. First-principles calculation revealed that Sb atoms are expected to be primarily located at the Si sites in Mg₂Si. The electrical resistivity, Seebeck coefficient, and thermal conductivity are strongly affected by the Sb concentration. The sample x = 0.02 shows a maximum value of the figure of merit ZT, which is 0.56 at 862 K.