热压工艺参数对n型和P型Bi2Te3基赝三元热电材料电学性能的影响

通过熔炼/研磨/热压方法制备了n型和p型赝三元Bi2Te3基的热压合金样品,测量了由不同工艺参数(热压温度、热压压力)制备的样品Seebeck系数和电导率.分析了热压参数对热电性能产生的影响.特别是发现了增加热压压力和热压温度会使n型和p型热压样品的Seebeck系数和电导率都有所提高,这与单晶和取向晶体材料的Seebeck系数和电导率变化趋势相反的规律显然不同,其结果对热压样品的电学性能提高有积极的影响.     

过量Zn对β-Zn4Sb3热电性能影响的研究

采用真空熔融缓冷方法制备了单相β-Zn₄Sb₃以及含有过量Zn的β-Zn₄Sb₃块体热电材料.在300—700K的温度范围内测试了材料的电导率、Seebeck系数和热导率，研究了β-Zn₄Sb₃化合物中过量Zn的分布状态及其对材料热电性能的影响规律.结果表明：过量的Zn作为第二相较均匀的分布在β-Zn₄Sb₃的晶界上，随着Zn含量增加，材料电导率和热导率上升，Seebeck系数下降，Zn第二相的引入能有效提高材料的功率因子，Zn过量2at%的材料在700K时其ZT值达到1.10. 关键词： 4Sb₃')" href="#">β-Zn₄Sb₃ 电导率 Seebeck系数     

制备工艺对p型碲化铋基合金热电性能的影响

利用区熔法、机械合金化、放电等离子烧结(SPS)技术、热压法等多种工艺制备了p型碲化铋基热电材料.在300—500K的温度范围内测量了各热电性能参数，包括电导率(σ)、塞贝克系数(α)和热导率(κ)，研究了制备工艺对热电性能的影响.结果表明，所制备的块体材料与同组成区熔晶体相比，性能优值ZT均有不同程度的提高.其中，利用区熔法结合SPS技术可获得热电性能最佳的块体材料，其ZT值达1.15. 关键词： 碲化铋 放电等离子烧结 区熔法 热电性能     

Ge掺杂n型Sn基Ⅷ型单晶笼合物的制备及热电传输特性

采用Sn自熔剂法制备了具有n型传导的Ⅷ型Ba₈Ga_16-xGe_xSn₃₀ （0 ≤ x ≤ 1.0）单晶笼合物,并对其结构和热电特性进行研究. 研究结果表明：Ge在单晶中的实际含量较少,随着掺杂量的增加样品的晶格常数略有减小,Ge掺杂后样品的载流子浓度较掺杂前低,迁移率增加;所有样品的Seebeck系数均为负值,且绝对值较未掺杂样品低,但Ge掺杂后样品的电导率提高了62%;x=0.5的样品在500 K附近取得最大ZT值1.25. 关键词： Ⅷ型笼合物 n型传导 热电性能     

(Sb2Te3)0.75(1－x)(Bi2Te3)0.25(1－x)(Sb2Se3)x机械合金化粉体的制备及其冷压烧结样品的热电性能研究

采用机械合金化法制备了p型赝三元(Sb₂Te₃-Bi₂Te₃-Sb₂Se₃)合金粉体，对其进行XRD分析表明Te，Bi，Sb，Se单质粉末，经100h球磨后实现了合金化；SEM分析表明所得机械合金化粉体材料颗粒均匀、细小，颗粒尺寸在10nm到100nm量级.使用这种粉体制备了冷压烧结块体样品，在室温下测量了温差电动势率(α)和电导率(σ)，研究了烧结温度对材料热电性能的影响，结果表明在低于300℃的烧结温区，样品室温下的热电性能随烧结温度的升高不断提高，功率因子(α²σ)由未烧结样品的0.59μW cm^-1K^-2升高到在300℃下烧结样品的15.9μW cm^-1K^-2，这一结果对确定材料的最佳烧结温度具有重要意义. 关键词： 赝三元热电材料 机械合金化 冷压 烧结     

Mg2Si的电子结构和热电输运性质的理论研究

利用全势线性缀加平面波法,对Mg₂Si的几何结构和电子结构进行了计算,得到了稳定的晶格参数以及能带和电子态密度.能带结构表明,Mg₂Si为间接带隙半导体,禁带宽度为020 eV.在此基础上利用玻尔兹曼输运理论和刚性带近似计算了材料的电导率、Seebeck系数和功率因子.结果表明,在温度为700 K时p型和n型掺杂的Mg₂Si功率因子达到最大时的最佳载流子浓度分别为7749×10¹⁹ cm^-3和 关键词： 2Si')" href="#">Mg₂Si 全势线性缀加平面波法 热电输运性质     

Nb掺杂对还原性烧结的TiO2-δ陶瓷的晶体结构及热电性能的影响

利用传统的固相反应法在还原性气氛1200 ℃下分别制备出不同Nb掺杂量的Ti_1-xNb_xO_2-δ陶瓷样品.样品的粉末X射线衍射(XRD)结果显示:Nb掺杂量x较低时样品为多相混合,当Nb掺杂量x>0.02时样品为单一的四方相金红石型结构.在室温到900 K的测试温区,测试了单相样品(x=0.02,0.03,0.04)的电导率、Seebeck系数和热导率.测试 关键词： 氧化钛陶瓷 热电性能 氧空位     

Ag掺杂对p型Pb0.5Sn0.5Te化合物热电性能的影响规律

采用熔融缓冷技术制备了不同Ag掺杂量的p型Ag_x(Pb_0.5Sn_0.5)_1-xTe化合物,系统地研究了Ag掺杂对所得材料的相组成、微结构及其热电传输性能.Ag的掺入显著增加了材料的空穴浓度,但是材料的空穴浓度远小于Ag作为单电子受主时理论空穴浓度,且在掺杂量为5%时未出现任何第二相,这表明Ag在可能进入晶格间隙位置而作为电子施主,起到补偿作用.随着Ag掺杂量的增加,样品的电导率逐渐增加,而Seebeck系数表现出复杂的变化趋势:在低于450 K时逐渐增加,而在温度大于450 K时逐渐降低,这主要源于材料复杂的价带结构.由于空穴浓度的优化和重空穴带的主导作用,1%Ag掺杂样品获得最大的功率因子,在750 K可达2.1 mW.m^-1.K^-2.此外,Ag的掺入引入的点缺陷大幅散射了传热声子,使得晶格热导率随着Ag掺量的增加逐渐降低.结果1%Ag掺杂样品在750 K时获得了最大的热电优值ZT=1.05,相比未掺样品提高了近50%,这一数值同商业应用的p型PbTe材料的性能相当.但是Sn取代显著降低了有毒重金属Pb的用量,这对PbTe基材料的商业化应用及其环境相适性具有重要意义.     

n型Bi2Te3基化合物的类施主效应和热电性能

晶粒细化是提高Bi₂Te₃基热电材料力学性能的重要方法,但晶粒细化过程中伴随的类施主效应严重劣化了材料的热电性能,并且一旦产生类施主效应,就很难通过简单的热处理等工艺消除.本文系统研究n型Bi₂Te₃基化合物烧结前粉体颗粒尺寸对材料类施主效应和热电性能的影响规律.随着颗粒尺寸减小,氧诱导的类施主效应明显增强,载流子浓度从10 M烧结样品的3.36×10¹⁹ cm^-3急剧增加到120 M烧结样品的7.33×10¹⁹ cm^-3,严重偏离最佳载流子浓度2.51×10¹⁹ cm^-3,热电性能严重劣化.当粉体颗粒尺寸为1—2 mm时,烧结样品的Seebeck系数为–195 μV/K,载流子浓度为3.36×10¹⁹ cm^-3,与区熔样品沿着ab面方向的Seebeck系数为–203 μV/K和载流子浓度为2.51×10¹⁹     

Bi2Te3 合金低温热电性能及冷能发电研究

利用机械合金化和冷压烧结法制备得到n型和p型Bi₂Te₃基热电材料,在80—300 K温度范围测量了电导率、Seebeck系数,结果表明其具有良好的低温热电性能.采用Bi₂Te₃基热电材料制备出半导体热电器件,并配合附属设备搭建出一套半导体温差发电装置.利用液氮汽化时释放的冷能,对半导体热电器件的发电性能进行实验研究,得出这种半导体热电器件输出电压、输出功率与电流关系式,测得最大的输出功率达到1.33 W,从而证明了冷     

Electronic structures and thermoelectric properties of La or Ce-doped Bi2Te3 alloys from first principles calculations

Thermoelectric properties of La or Ce-doped Bi₂Te₃ alloys were systematically investigated by ab initio calculations of electronic structures and Boltzmann transport equations. The Seebeck coefficient of p-type LaBi₇Te₁₂ and La₂Bi₆Te₁₂ was larger than that of Bi₂Te₃, because La doping increased the effective mass of carriers. On the other hand, the electrical conductivity of LaBi₇Te₁₂ and La₂Bi₆Te₁₂ decreased, which caused a reduction of power factor of these La-doped Bi₂Te₃ alloys in comparison with Bi₂Te₃. The influence of Ce doping on the band structure and thermoelectric properties of Bi₂Te₃ was similar to that of La doping. The theoretical calculation provided an insight into the transport properties of La or Ce-doped Bi₂Te₃-based thermoelectric materials.     

Hall mobility of amorphous Ge2Sb2Te5

The electrical conductivity, Seebeck coefficient, and Hall coefficient of three-micron-thick films of amorphous Ge₂Sb₂Te₅ have been measured as functions of temperature from room temperature down to as low as 200 K. The electrical conductivity manifests an Arrhenius behavior. The Seebeck coefficient is p-type with behavior indicative of multi-band transport. The Hall mobility is n-type and low (near 0.07 cm²/V s at room temperature).     

Preferential growth of Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> films with a nanolayer structure: enhancement of thermoelectric properties induced by nanocrystal boundaries

Preferential growth of different crystal planes in layered Bi₂Te₃ thin films with each layer <40 nm has been achieved by a simple magnetron co-sputtering method. The preferential growth of (015) plane or (001) was achieved at special depositing conditions due to the more sufficient growth along the in-plane direction induced by the enhanced diffusion of atoms and lower deposition rate. The Bi₂Te₃ film with preferential growth of (001) plane possesses about two times higher electrical conductivity and Seebeck coefficient as compared to the film with preferential growth of (015) plane, due to the greatly enhanced carrier mobility. Furthermore, the thermal conductivity has been suppressed due to more phonon scattering at grain boundaries, compared with ordinary Bi₂Te₃ alloys and films.     

Transport coefficients and defect structure of Sb2−xAgxTe3 single crystals

Incorporation of Ag in the crystal lattice of Sb₂Te₃ creates structural defects that have a strong influence on the transport properties. Single crystals of Sb_2−xAg_xTe₃ (x=0.0; 0.014; 0.018 and 0.022) were characterized by measurements of the temperature dependence of the electrical resistivity, Hall coefficient, Seebeck coefficient and thermal conductivity in the temperature range of 5-300 K. With an increasing content of Ag the electrical resistance, the Hall coefficient and the Seebeck coefficient all decrease. This implies that the incorporation of Ag atoms in the Sb₂Te₃ crystal structure results in an increasing concentration of holes. However, the doping efficiency of Ag appears to be only about 50% of the expected value. We explain this discrepancy by a model based on the interaction of Ag impurity with the native defects in the Sb_2−xAg_xTe₃ crystal lattice. Defects have a particularly strong influence on the thermal conductivity. We analyze the temperature dependence of the lattice thermal conductivity in the context of the Debye model. Of the various phonon scattering contributions, the dominant influence of Ag incorporation in the crystal lattice of Sb₂Te₃ is revealed to be point-defect scattering where both the mass defect and elastic strain play a pivotal role.     

Influence of negative pressure on thermoelectric properties of Sb2Te3

We investigated the influence of negative pressure on the electrical conductivity, the Seebeck coefficient, and the power factor of Sb₂Te₃. We performed first-principles calculations with the linearized-augmented plane-wave method considering negative hydrostatic pressure in the range from zero to −2 GPa and doping for electrons and holes up to 10²⁰ cm⁻³. Our results predict a significant increase of the Seebeck coefficient and the power factor under negative pressure for certain doping concentrations.     

Annealing effects on the structural and electrical transport properties of n-type Bi2Te2.7Se0.3 thin films deposited by flash evaporation

N-type Bi₂Te_2.7Se_0.3 thermoelectric thin films with thickness 800 nm have been deposited on glass substrates by flash evaporation method at 473 K. Annealing effects on the thermoelectric properties of Bi₂Te_2.7Se_0.3 thin films were examined in the temperature range 373-573 K. The structures, morphology and chemical composition of the thin films were characterized by X-ray diffraction, field emission scanning electron microscope and energy dispersive X-ray spectroscopy, respectively. Thermoelectric properties of the thin films have been evaluated by measurements of the electrical resistivity and Seebeck coefficient at 300 K. The Hall coefficients were measured at room temperature by the Van der Pauw method. The carrier concentration and mobility were calculated from the Hall coefficient. The films thickness of the annealed samples was measured by ellipsometer. When annealed at 473 K, the electrical resistivity and Seebeck coefficient are 2.7 mΩ cm and −180 μV/K, respectively. The maximum of thermoelectric power factor is enhanced to 12 μW/cm K².     

High pressure transport characteristics of Bi2Te3, Sb2Te3, and BiSbTe3

This paper presents ambient and high pressure measurements of transport properties of the Bi₂Te₃–Sb₂Te₃ series of materials. The electrical resistivity, thermal conductivity, and Seebeck coefficient have been measured on both end compounds and the direct solid solution of the two at pressure up to 10 GPa. An additional discussion involving the high pressure structure will be presented. From this, it was determined that these materials undergo at least two structural phase transitions between 0 and 20 GPa and a discussion is presented regarding this and the changes in the transport properties.     

Solvothermal preparation and characterization of nanocrystalline Bi2Te3 powder with different morphology

Bi₂Te₃-based alloys are currently best-known, technological important thermoelectric materials near room temperature. In this paper, nanocrystalline Bi₂Te₃ with different morphologies was synthesized by a solvothermal process based on the reaction between BiCl₃, Te, and KBH₄ in N,N-dimethylformamide at 100-180 °C. KBH₄ was used as a reducing agent. The products were characterized by X-ray diffraction and transmission electron microscopy (TEM). The particle morphologies and size are dependent on the reaction temperature and time. A possible formation mechanism is proposed.     

The effect of (00l) crystal plane orientation on the thermoelectric properties of Bi2Te3 thin film

Highly (00l)-oriented pure Bi₂Te₃ films with in-plane layered grown columnar nanostructure have been fabricated by a simple magnetron co-sputtering method. Compared with ordinary Bi₂Te₃ film and bulk materials, the electrical conductivity and Seebeck coefficient of such films have been greatly increased simultaneously due to raised carrier mobility and electron scattering parameter, while the thermal conductivity has been decreased due to phonon scattering by grain boundaries between columnar grains and interfaces between each layers. The power factor has reached as large as 33.7 μW cm⁻¹ K⁻², and the out-of-plane thermal conductivity is reduced to 0.86 W m⁻¹ K⁻¹. Our results confirm that tailoring nanoscale structures inside thermoelectric films effectively enhances their performances.