Frictional contact analysis of a rigid solid with periodic surface sliding on the thermoelectric material

Understanding and characterizing rough contact and wavy surfaces are essential for developing effective strategies to mitigate wear,optimize lubrication,and enhance the overall performance and durability of mechanical systems.The sliding friction contact problem between a thermoelectric(TE)half-plane and a rigid solid with a periodic wavy surface is the focus of this investigation.To simplify the problem,we utilize mixed boundary conditions,leading to a set of singular integral equations(SIEs)with the Hilbert kernels.The analytical solutions for the energy flux and electric current density are obtained by the variable transform method in the context of the electric and temperature field.The contact problem for the elastic field is transformed into the second-kind SIE and solved by the Jacobi polynomials.Notably,the smoothness of the wavy contact surface ensures that there are no singularities in the surface contact stress,and ensures that it remains free at the contact edge.Based on the plane strain theory of elasticity,the analysis primarily examines the correlation between the applied load and the effective contact area.The distribution of the normal stress on the surface with or without TE loads is discussed in detail for various friction coefficients.Furthermore,the obtained results indicate that the in-plane stress decreases behind the trailing edge,while it increases ahead of the trailing edge when subjected to TE loads.

Bilayer MSe_(2)(M=Zr,Hf,Mo,W)performance as a hopeful thermoelectric materials

Significant advancements in nanoscale material efficiency optimization have made it feasible to substantially adjust the thermoelectric transport characteristics of materials.Motivated by the prediction and enhanced understanding of the behavi-or of two-dimensional(2D)bilayers(BL)of zirconium diselenide(ZrSe_(2)),hafnium diselenide(HfSe_(2)),molybdenum diselenide(MoSe_(2)),and tungsten diselenide(WSe_(2)),we investigated the thermoelectric transport properties using information generated from experimental measurements to provide inputs to work with the functions of these materials and to determine the critical factor in the trade-off between thermoelectric materials.Based on the Boltzmann transport equation(BTE)and Barden-Shockley deformation potential(DP)theory,we carried out a series of investigative calculations related to the thermoelectric properties and characterization of these materials.The calculated dimensionless figure of merit(ZT)values of 2DBL-MSe_(2)(M=Zr,Hf,Mo,W)at room temperature were 3.007,3.611,1.287,and 1.353,respectively,with convenient electronic densities.In ad-dition,the power factor is not critical in the trade-off between thermoelectric materials but it can indicate a good thermoelec-tric performance.Thus,the overall thermal conductivity and power factor must be considered to determine the preference of thermoelectric materials.

Te基热电器件反常界面层生长行为及界面稳定性研究

单质Te具有优异的热电优值(ZT),但其与金属电极连接界面处的剧烈元素交互扩散及反应会引入较大的接触电阻率(ρc),导致器件的转换效率(η)较低。因此,寻找合适的阻挡层来优化Te与金属电极间的连接至关重要。本研究基于梯度结构报道了一种宽相场Ni-Te合金阻挡层NiTe_(2-m)(NixTe(x=0.500~0.908))。结果表明,当x=0.500时,Ni_(0.5)Te/Te_(0.985)Sb_(0.015)/Ni_(0.5)Te器件的界面处无任何反应层及微观缺陷,ρ_(c)小于10μΩ·cm^(2),η在180K温差(热端温度473K)时达到了理论值的75%。同时,界面具有良好的热稳定性,在473K老化期间,界面微观组织、ρ_(c)以及η无明显变化。当x>0.500时,界面反应层厚度随x增大而逐渐减小,即主导界面反应层生长行为的因素并非常规的界面反应能及浓度梯度等热力学因素。进一步分析表明,反常生长源于动力学因素中的“原子空位”对反应层生成的迟滞作用。

柔性PEDOT:PSS修饰Te纳米棒/PEDOT纳米线复合薄膜的制备及热电性能

通过改进的自组装胶束软模板法和湿化学法分别成功合成了聚(3,4-乙烯二氧噻吩)纳米线(PEDOT NW)和聚(3,4-乙烯二氧噻吩):聚苯乙烯磺酸(PEDOT:PSS)修饰的Te纳米棒(PC-Te),采用真空抽滤工艺制备了柔性自支撑PC-Te/PEDOT NW复合薄膜。通过透射电子显微镜等对PC-Te的显微结构进行表征,研究了PC-Te的添加量对复合薄膜的热电性能的影响规律。随着PC-Te含量的增加,复合薄膜的Seebeck系数增大,电导率减小,PC-Te含量为70%时,复合薄膜的功率因子的最大值达到47.4μW/mK^(2)(380 K)。该薄膜具有良好的柔性,弯曲500次后,其电阻变化率为9.2%。

Fundamental and progress of Bi_2Te_3-based thermoelectric materials

Thermoelectric materials,enabling the directing conversion between heat and electricity,are one of the promising candidates for overcoming environmental pollution and the upcoming energy shortage caused by the over-consumption of fossil fuels.Bi2Te3-based alloys are the classical thermoelectric materials working near room temperature.Due to the intensive theoretical investigations and experimental demonstrations,significant progress has been achieved to enhance the thermoelectric performance of Bi2Te3-based thermoelectric materials.In this review,we first explored the fundamentals of thermoelectric effect and derived the equations for thermoelectric properties.On this basis,we studied the effect of material parameters on thermoelectric properties.Then,we analyzed the features of Bi2Te3-based thermoelectric materials,including the lattice defects,anisotropic behavior and the strong bipolar conduction at relatively high temperature.Then we accordingly summarized the strategies for enhancing the thermoelectric performance,including point defect engineering,texture alignment,and band gap enlargement.Moreover,we highlighted the progress in decreasing thermal conductivity using nanostructures fabricated by solution grown method,ball milling,and melt spinning.Lastly,we employed modeling analysis to uncover the principles of anisotropy behavior and the achieved enhancement in Bi2Te3,which will enlighten the enhancement of thermoelectric performance in broader materials

Electronic Structure and Transport Coefficients of the Thermoelectric Materials Bi_2Te_3 from First-principles Calculations

The electronic structures of bulk Bi_2Te_3 crystals were investigated by the first-principles calculations.The transport coefficients including Seeback coefficient and power factor were then calculated by the Boltzmann theory,and further evaluated as a function of chemical potential assuming a rigid band picture.The results suggest that p-type doping in the Bi_2Te_3 compound may be more favorable than n-type doping.From this analysis results,doping effects on a material will exhibit high ZT.Furthermore,we can also find the right doping concentration to produce more efficient materials,and present the ＂advantage filling element map＂ in detail.

Probing the thermoelectric transport properties of n-type Bi_2Te_3 close to the limit of constitutional undercooling

Bulk n-type Bi2Te3 single crystals with optimized chemical composition were successfully prepared by a high temperature-gradient directional solidification method. We investigate the influence of alloy microstructure, chemical composition, and growth orientation on the thermoelectric transport properties. The results show that the composition of single-crystal Bi2Te3 alloy, along the c axis direction, could be slightly tuned by changing the growth rate of the crystal. At a rate of 18 mm/h, the formed Bi2Te3 crystal exhibits good thermoelectric properties. At 300 K, a maximum Seebeck coefficient of -245 μV/K and an electrical conductivity of 5.6 × 10 4 S/m are acquired. The optimal power factor is ob- tained as 3.3 × 10 -3 W/K2m, with a figure of merit of 0.74. It can be attributed to the increased tellurium allocation in the Bi2Te3 alloys, as verified well by the density functional theory caLculations.

Effects of Thickness and Temperature on Thermoelectric Properties of Bi2Te3-Based Thin Films

Bi_2Te_3 thin films and GeTe/B_2Te_3 superlattices of different thicknesses are prepared on the silicon dioxide substrates by magnetron sputtering technique and thermally annealed at 573 K for 30 min. Thermoelectric（TE）measurements indicate that optimal thickness and thickness ratio improve the TE performance of Bi_2Te_3 thin films and GeTe/B_2Te_3 superlattices, respectively. High TE performances with figure-of-merit（ZT） values as high as 1.32 and 1.56 are achieved at 443 K for 30 nm and 50 nm Bi_2Te_3 thin films, respectively. These ZT values are higher than those of p-type Bi_2Te_3 alloys as reported. Relatively high ZT of the GeTe/B_2Te_3 superlattices at 300-380 K were 0.62-0.76. The achieved high ZT value may be attributed to the unique nano-and microstructures of the films,which increase phonon scattering and reduce thermal conductivity. The results indicate that Bi_2Te_3-based thin films can serve as high-performance materials for applications in TE devices.

Effects of Electroless Plating with Cu Content on Thermoelectric and Mechanical Properties of p-type Bi0.5Sb1.5Te3 Bulk Alloys

Bi_（0.5）Sb_（1.5）Te_3/Cu core/shell powders were prepared by electroless plating and hydrogen reduction, and then sintered into bulk by spark plasma sintering. After electroless plating, with increasing the Cu content, the electrical conductivity keeps enhancing significantly. The highest electrical conductivity reaches 3341 S/cm at room temperature in Bi0.5Sb1.5Te3 with 0.67 wt% Cu bulk sample. Moreover, the lowest lattice thermal conductivity reaches 0.32 W/m·K at 572.2 K in Bi0.5Sb1.5Te3 with 0.67 wt% Cu bulk sample, which is caused by the scattering of the rich-copper particles with different dimensions and massive grain boundaries. According to the results, the ZT values of all Bi0.5Sb1.5Te3/Cu bulk samples have improved in a high temperature range. In Bi0.5Sb1.5Te3 with 0.15 wt% Cu bulk sample, the highest ZT value at 573.4 K is 0.81. When the Cu content increases to 0.67 wt%, the highest ZT value reaches 0.85 at 622.2 K. Meanwhile, the microhardness increases with increasing the Cu content.

Te和Y共掺杂提高n-Mg_(3.2)Sb_(1.5)Bi_(0.5)热电性能的研究

Mg_(3)Sb_(2)材料是优秀的中温区热电材料,具有极低的热导率,然而其载流子浓度偏低。通过机械合金化法结合放电等离子烧结(SPS)技术制备n型Mg_(3.2)Y_(0.05)Sb_(1.5)Bi_(0.5)Teδ样品,并研究了其热电传输性能。结果表明阴离子位掺杂元素Te可以进一步提高阳离子位掺杂的Mg_(3.2)Y_(0.05)Sb_(1.5)Bi_(0.5)材料的载流子浓度。载流子浓度从5.02×10^(19)cm-3增加到9.76×10^(19)cm-3,接近理论预测的最佳值,同时功率因子也从10.89μW·K^(-2)·cm^(-1)提高到15μW·K^(-2)·cm^(-1).此外,Te元素进入晶格后,材料的晶格热导率也有大幅的降低,从0.92 W·m^(-1)·K^(-1)降低到0.68 W·m^(-1)·K^(-1).载流子浓度最高的样品在750 K时zT峰值可达1.6,在300~750 K温度范围内的平均zT值可达1.0.本工作证明阳离子和阴离子位共同掺杂对Mg_(3)Sb_(1.5)Bi_(0.5)载流子浓度提高的效果优于单阳离子或单阴离子位掺杂,该掺杂方法有望应用到其它的热电材料性能的优化中。

Solid State Reaction Synthesis and Thermoelectric Properties ofMg_2Si doped with Sb and Te

Doped with Sb and Te, Mg2Si based compounds were prepared respectively by solid state reaction at 823 K for 8 h. Effects of dopants of Sb and Te on the structure and thermoelectric properties of the compounds were investigated. By calculating the values of the electrical conductivity for Sb-doped sample, the mechanism of electric conduction at 625 K is different. The figure of merit for sample doped with 0.4 wt% Te at500K is 2.4 × 10-3W/mK2,and it reaches 3. 3 ×10-3 W/mK2 at 650K for the sample doped with 0. 5wt% Sb. The values are more than 1.4 times and 2.3 times of the pure Mg2 Si sample.

Se substitution and micro-nano-scale porosity enhancing thermoelectric Cu2Te

Binary Cu-based chalcogenide thermoelectric materials have attracted a great deal of attention due to their outstanding physical properties and fascinating phase sequence.However,the relatively low figure of merit z T restricts their practical applications in power generation.A general approach to enhancing z T value is to produce nanostructured grains,while one disadvantage of such a method is the expansion of grain size in heating-up process.Here,we report a prominent improvement of z T in Cu2Te（0.2）Se（0.8）,which is several times larger than that of the matrix.This significant enhancement in thermoelectric performance is attributed to the formation of abundant porosity via cold press.These pores with nano-to micrometer size can manipulate phonon transport simultaneously,resulting in an apparent suppression of thermal conductivity.Moreover,the Se substitution triggers a rapid promotion of power factor,which compensates for the reduction of electrical properties due to carriers scattering by pores.Our strategy of porosity engineering by phonon scattering can also be highly applicable in enhancing the performances of other thermoelectric systems.

Improved thermoelectric performance in p-type Bi_(0.48)Sb_(1.52)Te_3 bulk material by adding MnSb_2Se_4

Bismuth telluride（Bi2Te3） based alloys, such as p-type Bi（0.5）Sb（1.5）Te3, have been leading candidates for near room temperature thermoelectric applications. In this study, Bi（0.48）Sb（1.52）Te3 bulk materials with MnSb2Se4 were prepared using high-energy ball milling and spark plasma sintering（SPS） process. The addition of MnSb2Se4 to Bi（0.48）Sb（1.52）Te3 increased the hole concentration while slightly decreasing the Seebeck coefficient, thus optimising the electrical transport properties of the bulk material. In addition, the second phases of MnSb2Se4 and Bi（0.48）Sb（1.52）Te3 were observed in the Bi（0.48）Sb（1.52）Te3 matrix. The nanoparticles in the semi-coherent second phase of MnSb2Se4 behaved as scattering centres for phonons,yielding a reduction in the lattice thermal conductivity. Substantial enhancement of the figure of merit, ZT, has been achieved for Bi（0.48）Sb（1.52）Te3 by adding an Mn（0.8）Cu（0.2）Sb2Se4（2mol%） sample, for a wide range of temperatures, with a peak value of 1.43 at 375 K, corresponding to -40% improvement over its Bi（0.48）Sb（1.52）Te3 counterpart. Such enhancement of the thermoelectric（TE） performance of p-type Bi2Te3 based materials is believed to be advantageous for practical applications.

Thermoelectric Properties of N-typer Bi_2Te_3-PbTe Graded Thermoelectric Materials with Different Barriers

In order to investigate the adaptability of thermoelectric materials system with different barriers to functional graded thermoelectric materials, n-type Bi2Te, and PbTe two segments graded thermoelectric materials (GTM) with different barriers were fabricated by conventional hot pressing method. Metals Cu, Al, Fe, Co and Ni were used as barriers between two segments. The effects of different barriers on thermoelectric properties of GTM were investigated. The phase and crystal structures were determined by x-ray diffraction analysis (XRD). The distributions of different compositions were analyzed by electron microprobe analysis (EMA). The thermoelectric properties were measured at 303 K along the direction parallel to the pressing direction. The electric conductivity of samples was measured at 303 K by the four-probe technique. To measure the Seebeck coefficient, heat was applied to the samples, which were placed between two Cu discs. The thermoelectric electromotive force (E) was measured upon applying small temperature differences (DeltaT<275 K) between the both ends of the samples. The Seebeck coefficient of the samples was determined from the E/&UDelta;T.

二甲基亚砜有机溶液中Sb-Te薄膜热电材料的电沉积制备

采用循环伏安以及阴极极化曲线的测试方法分析了二甲基亚砜有机溶液中纯Sb、纯Te、Sb-Te二元体系在Au电极上的还原过程。结合分析结果采用直流恒电位方式电沉积制备了Sb-Te二元薄膜热电材料,并采用X射线衍射(XRD)、扫描电子显微镜(SEM)、能谱仪(EDS)以及塞贝克系数测试系统对不同电位下制备出的Sb-Te二元薄膜热电材料的物相、形貌、组成、热电性能等进行了表征。结果表明:在Au电极上Sb(Ⅲ)、Te(Ⅳ)离子的氧化还原行为均为不可逆过程,随着电位的不断负移,所制备出的薄膜热电材料表面粗糙度也在不断加大,Sb、Te元素原子百分含量的比值在不断下降,不同电位下沉积出的材料均为P型热电材料。

A Thermoelectric Transducer Based on Bismuth Telluride Thin Films for H_2 Gas Sensing

We have developed a novel thermoelectric gas sensors based on bismuth telluride thin films.These sensors were employed for sensing different concentrations of H_2 gas.Radio frequency (R.F.) magnetron sputtering was employed to deposit the bismuth telluride (Bi_2Te_3) thin films.The morphology of such thin films was investigated and responses of the thermoelectric devices to H_2 were studied.

Thermoelectric Transport by Surface States in Bi2Se3-Based Topological Insulator Thin Films

We develop a tractable theoretical model to investigate the thermoelectric （TE） transport properties of surface states in topological insulator thin films （TITFs） of Bi2Sea at room temperature. The hybridization between top and bottom surface states in the TITF plays a significant role. With the increasing hybridization-induced surface gap, the electrical conductivity and electron thermal conductivity decrease while the Seebeck coefficient increases. This is due to the metal-semiconductor transition induced by the surface-state hybridization. Based on these TE transport coefficients, the TE figure-of-merit ZT is evaluated. It is shown that ZT can be greatly improved by the surface-state hybridization. Our theoretical results are pertinent to the exploration of the TE transport properties of surface states in TITFs and to the potential application of Bi2Sea-based TITFs as high-performance TE materials and devices.

Thermoelectric properties of Bi_(0.5)Sb_(1.5)Te_3/polyaniline composites prepared by mechanical blending and in-situ polymerization

Bi 0.5 Sb 1.5 Te 3/polyaniline composites were prepared by mechanical blending and in situ polymerization, and their transport properties were measured. It was found that for the composites with 1%, 3%, 5% and 7% polyaniline (mass fraction) respectively, which were prepared by mechanical blending, the power factors decrease by about 30%, 50%, 55% and 65% compared with the Bi 0.5 Sb 1.5 Te 3 samples, which is mainly due to the remarkable decreases of the electrical conductivity. The electrical conductivity and power factor of the composites samples with 7% polyaniline prepared by in situ polymerization are higher by about 65% and 60%, respectively, than that of the corresponding samples prepared by mechanical blending.

Thermoelectric Performance of Micro/Nano-Structured Bismuth-Antimony-Telluride Bulk from Low Cost Mechanical Alloying

In this work, micro/nano-structured Bi0.5Sb1.5Te3bulk thermoelectric materials were synthesized by mechanical alloying from elemental shots of Bi, Sb, and Te. Cold pressing and subsequent heat treatments with hydrogen reduction were used to form bulk solid samples with good thermoelectric properties in the temperature range around 75℃to 100℃. In comparison to crystal growth methods and chemical solution synthesis, the reported technique can be readily implemented for mass production with relatively low cost.

Fabrication and Characterization of PLD-Grown Bismuth Telluride (Bi₂Te₃) and Antimony Telluride (Sb₂Te₃) Thermoelectric Devices

We report on the fabrication and characterization of multi-leg bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) thermoelectric devices. The two materials were deposited, on top of SiO2/Si substrates, using Pulsed Laser Deposition (PLD). The SiO2 layer was used to provide insulation between the devices and the Si wafer. Copper was used as an electrical connector and a contact for the junctions. Four devices were built, where the Bi2Te3 and Sb2Te3 were deposited at substrate temperatures of 100&deg;C, 200&deg;C, 300&deg;C and 400&deg;C. The results show that the device has a voltage sensitivity of up to 146 &mu;V/K and temperature sensitivity of 6.8 K/mV.