Thermoelectric properties of Bi2Se3/Bi2Te3/Bi2Se3 and Sb2Te3/Bi2Te3/Sb2Te3 quantum well systems

In this work, we develop a theory of thermoelectric transport properties in two-dimensional semiconducting quantum well structures. Calculations are performed for n-type 0.1 wt.% CuBr-doped Bi₂Se₃/Bi₂Te₃/Bi₂Se₃ and p-type 3 wt.% Te-doped Sb₂Te₃/Bi₂Te₃/Sb₂Te₃ quantum well systems in the temperature range 50–600 K. It is found that reducing the well thickness has a pronounced effect on enhancing the thermoelectric figure of merit (ZT). For the n-type Bi₂Se₃/Bi₂Te₃/Bi₂Se₃ with 7 nm well width, the maximum value of ZT is estimated to be 0.97 at 350 K and for the p-type Sb₂Te₃/Bi₂Te₃/Sb₂Te₃ with well width 10 nm the highest value of the ZT is found to be 1.945 at 440 K. An explanation is provided for the resulting higher ZT value of the p-type system compared to the n-type system.     

熔体旋甩法合成n型(Bi_(0.85)Sb_(0.15))_2(Te_(1-x)Se_x)_3化合物的微结构及热电性能

采用熔体旋甩结合放电等离子烧结(MS-SPS)技术制备了单相n型四元(Bi0.85Sb0.15)2(Te1-xSex)3(x=0.15,0.17,0.19,0.21)化合物,并对所得样品的微结构和热电传输性能进行了系统研究.样品自由断裂面的场发射扫描电子显微镜及抛光面的背散射电子成分分析表明:块体材料晶粒细小,晶粒排列紧密,成分分布均匀且相结构单一,样品中存在大量10—100nm的层状结构.随着Se含量x的增加,样品的电导率和热导率逐渐增加,而Seebeck系数逐渐降低.相比商业应用的区熔材料,MS-SPS方法合成的高Se组成的样品均在425K后表现出更高的ZT值,其中(Bi0.85Sb0.15)2(Te0.83Se0.17)3样品具有最高的ZT值,在360K可达到0.96,并在320—500K均保持较高的ZT值,500K时其ZT值相比区熔材料提高了48%.此外,通过调节Se的含量,可以有效地调控材料的ZT峰值出现的温度段,这对多级或梯度热电器件的制备具有重要意义.     

Improved thermoelectric performance of n-type Mg3Sb2–Mg3Bi2 alloy with Co element doping

n-type Mg₃Sb₂–Mg₃Bi₂ alloy shows as a potential new thermoelectric material (TE) and has been widely researched recently. The pure phase n-type Mg_3·20(Sb_0·3Bi_0.7)_1.99Te_0.01 were prepared by adjusting Mg content with the Bi impurity phase being effectively suppressed. Then, Co element was doped into the pure phase and the electrical conductivity of samples were improved. With a high power factor of 20.3 μW cm⁻¹K⁻² for Mg_3·185Co_0·015(Sb_0·3Bi_0.7)_1.99Te_0.01 at 525 K. Additionally, it was found that the phonon scattering is enhanced due to the larger atomic mass of Co comparing to Mg and the lattice thermal conductivity is reduced. As a result, a high ZT value of ~ 1.03 at 525 K is achieved for the Mg_3·185Co_0·015(Sb_0·3Bi_0.7)_1.99Te_0.01.     

Investigation of the possibilities for increasing the thermoelectric figure of merit of nanostructured materials based on Bi2Te3-Sb2Te3 solid solutions

The transport coefficients and thermoelectric figure of merit ZT for bulk nanostructured materials based on Bi₂Te₃-Sb₂Te₃ solid solutions have been investigated theoretically. Similar materials prepared by rapid quenching of the melt with the subsequent grinding and sintering contain amorphous and nanocrystalline regions with different sizes of particles. According to the performed estimations, the thermoelectric figure of merit of the amorphous phase can exceed the value of ZT for the initial solid solution by a factor of 2?C3 primarily due to the significant decrease in the thermal conductivity. The effective transport coefficients of the medium as a whole have also been investigated as a function of the parameters of each phase, and the concentration range of the amorphous phase, which corresponds to the effective values ZT > 1, has been determined.     

Doping effects on the thermoelectric properties of Cu-intercalated Bi2Te2.7Se0.3

We herein report an enhancement of the thermoelectric performance of spark plasma sintered polycrystalline n-type Bi₂Te_2.7Se_0.3 by the intercalation of Cu and the doping of Al on Bi-sites. Through the intercalation of a small amount of Cu (0.008), the reproducibility could be significantly improved, with ZT was enhanced from 0.64 to 0.73 at 300 K due to the reduced lattice thermal conductivity benefiting from intensified point-defect phonon scattering. We also found that Al is an effective doping element for power factor enhancement and for reducing the lattice thermal conductivity of Cu-intercalated Bi₂Te_2.7Se_0.3. With these synergetic effects, an enhanced ZT values of 0.78 at 300 K and 0.81 at 360 K were obtained in 1 at% Al-doped Cu_0.008Bi₂Te_2.7Se_0.3 (Cu_0.008Bi_1.98Al_0.02Te_2.7Se_0.3).     

An analysis of the thermoelectric efficiency of n-(Bi,Sb)2(Te,Se,S)3 solid solutions within an isotropic scattering model

A study is reported on the thermoelectric properties of n-type solid solutions Bi₂Te_3?y Se_y (y=0.12, 0.3, 0.36), Bi_2?x Sb_xTe_3?y Se_y (x=0.08, 0.12; y=0.24, 0.36), and Bi₂Te_3?z S_z (z=0.12, 0.21) as functions of carrier concentration within the 80-to 300-K range. It has been established that the highest thermoelectric efficiency Z is observed in the Bi₂Te_3?y Se_y (y=0.3) solid solution containing excess Te at optimum carrier concentrations (0.35×10¹⁹ cm^?3) and at temperatures from 80 to 250 K. The increase in Z in the Bi₂Te_3?y Se_y solid solution compared with Bi_2?x Sb_xTe_3?y Se_y and Bi₂Te_3?z S_z is accounted for by the high mobility μ₀, an increase in the effective mass m/m ₀ with decreasing temperature, the low lattice heat conductivity κ_L, and the weak anisotropy of the constant-energy surface in a model assuming isotropic carrier scattering.     

Electrical transport and high thermoelectric properties of PbTe doped with Bi2Te3 prepared by HPHT

In this paper, n-type lead telluride (PbTe) compounds doped with Bi₂Te₃ have been successfully prepared by high pressure and high temperature (HPHT) technique. The composition-dependent thermoelectric properties of PbTe doped with Bi₂Te₃ have been studied at room temperature. The figure-of-merit, Z, for PbTe is very sentivite to the dopants, which could be improved largely although the doped content of Bi₂Te₃ is very small (<0.08 mol%). In addition, the maximum value reaches to 9.3×10⁻⁴ K⁻¹, which is about 20% higher than that of PbTe alloyed with Bi₂Te₃ sintered at ambient pressure (7.6×10⁻⁴ K⁻¹) and several times higher than that of small grain size PbTe containing other dopants. The improved thermoelectric performance in this study may be due to the effect of high pressure and the low lattice thermal conductivity resulting from Bi₂Te₃ as source of dopants.     

Annealing temperature influence on electrical properties of ion beam sputtered Bi2Te3 thin films

Ion beam sputtering process was used to deposit n-type fine-grained Bi₂Te₃ thin films on BK7 glass substrates at room temperature. In order to enhance the thermoelectric properties, thin films are annealed at the temperatures ranging from 100 to 400 °C. X-ray diffraction (XRD) shows that the films have preferred orientations in the c-axis direction. It is confirmed that grain growth and crystallization along the c-axis are enhanced as the annealing temperature increased. However, broad impurity peaks related to some oxygen traces increase when the annealing temperature reached 400 °C. Thermoelectric properties of Bi₂Te₃ thin films were investigated at room temperature. The Bi₂Te₃ thin films, including as-deposited, exhibit the Seebeck coefficients of −90 to −168 μV K⁻¹ and the electrical conductivities of 3.92×10²-7.20×10² S cm⁻¹ after annealing. The Bi₂Te₃ film with a maximum power factor of 1.10×10⁻³ Wm⁻¹ K⁻² is achieved when annealed at 300 °C. As a result, both structural and transport properties have been found to be strongly affected by annealing treatment. It was considered that the annealing conditions reduce the number of potential scattering sites at grain boundaries and defects, thus improving the thermoelectric properties.     

Changes in the electronic properties of Bi2X3 (X: Se, Te) single crystals due to intercalation

Bi₂Se₃ and Bi₂Te₃ are layered semiconductors n-type and p-type, respectively, which belong to the family of thermoelectric materials. In this work we examine the insertion of Cu in Bi₂Te₃ and Bi₂Se₃ single crystals through an intercalation reaction. The inserted Cu acting as donor enhances the n-type character of Bi₂Se₃ while changing the native p-type character of Bi₂Te₃ to n-type. The spatial distribution of the intercalated species was monitoring by X-ray microanalysis and microscopic IR reflectivity measurements. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Electrophysical parameters of <Emphasis Type="Italic">c</Emphasis>-oriented Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> films with a low concentration of antistructural defects

Epitaxial c-oriented Bi₂Te₃ films 1.2 μm in thickness are grown by the hot wall method for a low supersaturation of the vapor phase over the surface of mica substrates. The hexagonal unit cell parameters a = 4.386 Å and c = 30.452 Å of the grown films almost coincide with the corresponding parameters of stoichiometric bulk Bi₂Te₃ crystals. At T = 100 K, the Hall concentration of electrons in the films is on the order of 8 × 10¹⁸ cm^?3, while the highest values of the thermoelectric coefficient (α ≈ 280 μV K^?1) are observed at temperatures on the order of 260 K. Under impurity conduction conditions, conductivity σ of the films increases upon cooling in inverse proportion to the squared temperature. In the temperature range 100–200 K, thermoelectric power parameter α²σ of Bi₂Te₃ films has values of 80–90 μW cm^?1 K^?2.     

High-pressure thermoelectric characteristics of Bi2Te3 semiconductor with different charge carrier densities

The measurements of the absolute values of the thermopower and of the relative electrical resistance have been performed for n type Bi₂Te₃ under hydrostatic pressure up to 9 GPa at room temperature. Under pressures exceeding 5 GPa and up to the phase transition (at 7 GPa), the samples with the charge carrier density below 10^?19 cm^?3 exhibit an anomalous growth of the thermopower. For the purest sample (n = 10^?18 cm^?3), the thermopower is as high as +150 μV/K. The pressure dependence of the electrical resistance for n-Bi₂Te₃ does not exhibit any anomalies up to the pressure corresponding to the phase transition (7 GPa). Thus, the state with the giant thermoelectric efficiency is found in Bi2Te3 under pressure before the phase transition.     

Thermoelectric properties of multicomponent solid solutions based on bismuth and antimony chalcogenides with n-type conduction in the region of impurity and mixed conduction

The thermoelectric properties of Bi_2?x Sb _x Te_{3 ? y ? z} Se _y S _z solid solutions are studied in the temperature range 300–450 K. It is shown that, as the number of atoms involved in substitutions in both sublattices during the formation of a solid solution increases, the maximum in the temperature dependence of the thermopower coefficient and the minimum in the temperature dependence of the thermal conductivity shift toward higher temperatures as a result of an increase in the band gap. As the charge carrier concentration in the sample of a solid solution increases, the onset of mixed conduction shifts toward higher temperatures, which leads to an additional decrease in the thermal conductivity at a fixed temperature. The observed temperature dependences of the thermoelectric properties of the Bi_{2 ? x} Sb _x Te_{3 ? y ? z} Se _y S _z solid solutions bring about a shift of the maximum in the thermoelectric efficiency toward higher temperatures as the number of atoms involved in the substitution increases.     

Fermi surface and thermoelectric power of (Bi1−x Sbx)2Te3<Ag, Sn> mixed crystals

The Fermi surface anisotropy of (Bi_1?x Sb_x)₂Te₃ single crystals (0.25 ≤ x ≤ 1) was studied by analyzing the angular dependence of the frequency of Shubnikov-de Haas oscillations and the effect of tin and silver doping on the thermoelectric power in these crystals in the temperature range 77 ≤ T ≤ 300 K. It was shown that silver doping of (Bi_1?x Sb_x)₂Te₃ mixed crystals produces acceptors, while silver in Bi₂Te₃ acts as a donor. Tin also exhibits acceptor properties. Both tin and silver doping of p-(Bi_1?x Sb_x)₂Te₃ mixed crystals decrease the thermoelectric power due to an increase in the hole concentration.     

High temperature thermoelectric properties of Ca1−xBixMn1−yV yO3−δ (0≤x=y≤0.08)

CaMnO_3?δ with complex additives Bi₂O₃–V ₂O₅ were prepared by the solid-state reaction. The crystal structures of the Ca_1?xBi_xMn_1?yV _yO_3?δ (0≤x=y≤0.08) solid solutions were determined by means of the powder X-ray diffraction (XRD) using Rietan 2000 program and the high temperature thermoelectric properties were also investigated. Perovskite-type Ca_1?xBi_xMn_1?yV _yO_3?δ solid solutions are n-type semiconductors. The lattice parameters increase with increasing dopant level. The high temperature thermoelectric properties are improved due to Bi₂O₃–V ₂O₅ simultaneous doping. A maximum ZT value reaches to 0.21 for electron-doped Ca_0.96Bi_0.04Mn_0.96V _0.04O_3?δ at 1050 K, which is about twice as high as that of CaMnO_3?δ. The thermal shock resistance at temperatures between 20 and 450 ^°C is also highly improved.     

Electrodeposition of BixSb2−xTey thermoelectric thin films from nitric acid and hydrochloric acid systems

The electrochemical behaviors of Bi^III, Te^IV and Sb^III single ions and their mixtures were investigated in nitric acid and hydrochloric acid system separately. Based on which, Bi_xSb_2−xTe_y thermoelectric films were prepared by potentiostatic electrodeposition from the solutions with different concentrations of Bi^III, Te^IV and Sb^III in the two acid systems. The morphologies, compositions, structures, Seebeck coefficients and resistivities of the deposited thin films were characterized and compared by ESEM (or FESEM), EDS, XRD, Seebeck coefficient measurement system and four-probe resistivity measuring device respectively. The results show that although Bi_xSb_2−xTe_y thermoelectric thin film which structure is consistent with the standard pattern of Bi_0.5Sb_1.5Te₃ can be gained in both of the two acid solutions by adjusting the deposition potential, their morphologies and thermoelectric properties have big differences in different acid solutions.     

Optical and thermoelectric characterizations of electroplated n-Bi2(Te0.9Se0.1)3

Bismuth selenotelluride (Bi₂(Te_0.9Se_0.1)₃) films were electrodeposited at constant current density from acidic aqueous solutions with Arabic gum in order to produce thin films for miniaturized thermoelectric devices. X-ray fluorescence spectroscopy determined film compositions. X-ray diffraction pattern shows that the films as deposited are polycrystalline, isostructural to Bi₂Te₃ and covered by crystallites. Mueller-matrix analysis reveals that the electroplated layers are optically like an isotropic medium. Their pseudo-dielectric functions were determined using mid-infrared spectroscopic ellipsometry. Tauc-Lorentz combined with Drude dispersion relations were successfully used. The energy band gap E_g was found to be about 0.15 eV. Moreover, the fundamental absorption edge was described by an indirect optical band-to-band transition. From Seebeck coefficient measurement, films exhibit n-type charge carrier and the value of thermoelectric power is about −40 μV/K.     

TeI4掺杂量对n型Bi2Te3基烧结材料热电性能的影响

采用区熔法结合放电等离子体快速烧结(SPS)技术制备了n型Bi₂Te₃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)，研究了掺杂剂TeI₄的含量(质量百分比分别为0，0.05，0.08，0.10，0.13和0.15wt%)对热电性能的影响.结果表明：试样的载流子浓度(n)随TeI₄含量增加而增大，使电导率增大、塞贝克系数的绝对值先增大而后减小，从而导致品质因子(α²σ)呈先增加后降低的变化趋势；同时，由于异质离子(I^-)以及载流子对声子的散射作用增强，可显著降低其晶格热导率.烧结材料的性能优值(ZT=α²σT/κ)对应于TeI₄含量为0.08wt%有其最大值，约为0.92.此外，烧结材料的抗弯强度增加至80MPa左右，从而可以显著改善材料的可加工性以及元器件的使用可靠性. 关键词： 2Te₃')" href="#">Bi₂Te₃ 放电等离子体快速烧结 热电性能     

纳米结构碲化铋合金的制备及电热输运特性

采用惰性气体保护蒸发-冷凝法制备了纳米Bi及Te粉末, 结合机械合金化和放电等离子烧结技术, 在不同烧结温度下制备出了单一物相且具有纳米层状结构及孪晶亚结构的n型Bi₂Te₃块体材料, 并系统研究了块体材料的晶粒尺度、微结构及其对电热传输特性的影响. SEM, TEM分析结果表明, 以纳米粉末为原料, 通过有效控制工艺条件, 可以制备出具有纳米层状结构Bi₂Te₃合金块体材料, 同时纳米层状结构中存在孪晶亚结构; 热电性能测试结果表明, 具有纳米层状结构及孪晶亚结构的块体试样与粗晶材料相比, 热导率大幅度降低, 在423 K附近, 热导率由粗晶材料的1.80 W/mK降至1.19 W/mK, 晶格热导率从1.16 W/mK降至0.61 W/mK, 表明纳米层状结构与孪晶亚结构共存, 有利于进一步提高声子散射, 降低晶格热导率. 其中在693 K放电等离子烧结后的试样于423K附近取得最大值的无量纲热电优值(ZT), 达到0.74.     

Laser-induced forward transfer of intact chalcogenide thin films: resultant morphology and thermoelectric properties

We present a laser-based transfer method for the novel application of fabricating elements for planar thermoelectric devices. Thin films of thermoelectric chalcogenides (Bi₂Te₃, Bi₂Se₃ and Bi_0.5Sb_1.5Te₃) were printed via laser-induced forward transfer (LIFT) onto polymer-coated substrates over large areas of up to ～15 mm² in size. A morphological study showed that it was possible to partially preserve the polycrystalline structure of the transferred films. The films’ Seebeck coefficients after LIFT transfer were measured and resulted in ?49±1 μV/K, ?93±8 μV/K and 142±3 μV/K for Bi₂Te₃, Bi₂Se₃ and Bi_0.5Sb_1.5Te₃, respectively, which were found to be ～23±6 % lower compared to their initial values. This demonstration shows that LIFT is suitable to transfer sensitive, functional semiconductor materials over areas up to ～15 mm² with minimal damage onto a non-standard polymer-coated substrate.     

Bi-Sb-Te基热电薄膜温差电池离子束溅射制备与表征

本文采用离子束溅射Bi/Te和Sb/Te二元复合靶,直接制备n型Bi₂Te₃热电薄膜和p型Sb₂Te₃热电薄膜.在退火时间同为1 h的条件下,对所制备的Bi₂Te₃薄膜和Sb₂Te₃薄膜进行不同温度的退火处理,并对其热电性能进行表征.结果表明,在退火温度为150 ℃时,制备的n型Bi₂Te₃关键词： 薄膜温差电池 2Te₃薄膜')" href="#">Sb₂Te₃薄膜 2Te₃薄膜')" href="#">Bi₂Te₃薄膜 离子束溅射