GaInX_3(X=S,Se,Te):Ultra-low thermal conductivity and excellent thermoelectric performance

Seeking intrinsically low thermal conductivity materials is a viable strategy in the pursuit of high-performance thermoelectric materials.Here,by using first-principles calculations and semiclassical Boltzmann transport theory,we systemically investigate the carrier transport and thermoelectric properties of monolayer Janus GaInX_(3)(X=S,Se,Te).It is found that the lattice thermal conductivities can reach values as low as 3.07 W·m^(-1)·K^(-1),1.16 W·m^(-1)·K^(-1)and 0.57 W·m^(-1)·K^(-1)for GaInS_(3),GaInSe_(3),and GaInTe_(3),respectively,at room temperature.This notably low thermal conductivity is attributed to strong acoustic-optical phonon coupling caused by the presence of low-frequency optical phonons in GaInX_(3) materials.Furthermore,by integrating the charac teristics of electronic and thermal transport,the dimensionless figure of merit ZT can reach maximum values of 0.95,2.37,and 3.00 for GaInS_(3),GaInSe_(3),and GaInTe_(3),respectively.Our results suggest that monolayer Janus GaInX_(3)(X=S,Se,Te)is a promising candidate for thermoelectric and heat management applications.

Diameter-dependent ultra-high thermoelectric performance of ZnO nanowires

Zinc oxide(ZnO)shows great potential in electronics,but its large intrinsic thermal conductivity limits its thermoelectric applications.In this work,we explore the significant carrier transport capacity and diameter-dependent thermoelectric characteristics of wurtzite-ZnO(0001)nanowires based on first-principles and molecular dynamics simulations.Under the synergistic effect of band degeneracy and weak phonon-electron scattering,P-type(ZnO)_(73) nanowires achieve an ultrahigh power factor above 1500μW·cm^(-1)·K^(-2)over a wide temperature range.The lattice thermal conductivity and carrier transport properties of ZnO nanowires exhibit a strong diameter size dependence.When the ZnO nanowire diameter exceeds 12.72A,the carrier transport properties increase significantly,while the thermal conductivity shows a slight increase with the diameter size,resulting in a ZT value of up to 6.4 at 700 K for P-type(ZnO)_(73).For the first time,the size effect is also illustrated by introducing two geometrical configurations of the ZnO nanowires.This work theoretically depicts the size optimization strategy for the thermoelectric conversion of ZnO nanowires.

Effect of Molecular Weight on Thermoelectric Performance of P3HT Analogues with 2-Propoxyethyl Side Chains

By replacing hexyl chains in poly(3-hexylthiophene)(P3HT)with 2-propoxyethyls,four poly(3-(2-propoxyethyl)thiophene)(P3POET)homopolymers with comparable polydispersity indexes(PDI)and regioregularities were prepared herein in addition with step increment of about 7 kDa on numberaverage molecular weight(M_(n))from around 11 to 32 kDa(accordingly denoted as P11k,P18k,P25k,and P32k).When doped in film by FeCl_(3)at the optimized conditions,the maximum power factor(PF_(max))increases greatly from 4.3μW·m^(-1)·K^(-2)for P11k to 8.8μW·m^(-1)·K^(-2)for P18k,and further to 9.7μW·m^(-1)·K^(-2)for P25k,followed by a slight decrease to 9.2μW·m^(-1)·K^(-2)for P32k.The close Seebeck coefficients(S)at PF_(max)are observed in these doped polymer films due to their consistent frontier orbital energy levels and Fermi levels.The main contribution to this PF_(max)evolution thus comes from the corresponding conductivities(σ).Theσvariation of the doped films can be rationally correlated with their microstructure evolution.

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.

Control of interfacial reaction and defect formation in Gd/Bi_(2)Te_(2.7)Se_(0.3) composites with excellent thermoelectric and magnetocaloric properties

The method to combine thermoelectric(TE)and magnetocaloric(MC)cooling techniques lies in developing a new material that simultaneously possesses a large TE and good MC cooling performance.In this work,using n-type Bi_(2)Te_(2.7)Se_(0.3)(BTS)as the TE base material and Gd as the second-phase MC material,Gd/BTS composites were prepared by the spark plasma sintering method.In the composites,interfacial reaction between Gd and BTS was identified,resulting in the formation of Gd Te,which has a large impact on the electron concentration through the adjustment of defect concentration.The MC/TE composite containing 2.5 wt%Gd exhibited a ZT value of 0.6 at 300 K,essentially retaining the original TE performance,while all the composites largely maintained the excellent MC performance of Gd.This work provides a potential pathway to achieving high performance in MC/TE composites.

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.

Performance analysis of aircraft low-power thermoelectric refrigeration system

An optimal design method for an aircraft low-power thermoelectric refrigeration system（TRS）is proposed using an existing experimental model as the research platform under given aircraft flight conditions.The variation curves of the cooling capacities and the refrigeration coefficients of the system running at three flight altitudes are investigated.The performance of the system is evaluated by the minimum-entropy-generation method and the performance penalty is also calculated.The power variation curves of the cooling system are obtained by an electric power experiment.The peak values of these curves are less than the maximal electric power supply of airborne equipment,proving that the use of the low-power TRS for airborne equipment is feasible.The COP,cooling capacity and entropy generation of the system are relative to the flight altitude and the current of the TRS.Through the analyses of these data,the optimal values of the COP are obtained,and the optimization measures are proposed to maximize the use of the advantages of the TRS.

A New Technology to Measure the Thermoelectric Performance of Nanowire Array Structure

Recently, the study on one-dimensional thermoelectric materials is getting more and more attention. For those one-dimensional thermoelectric materials with nanowire array structure fabricated with alumina film as template, its thickness is often in the range of 10 to several tens micrometers, and the conventional measurement cannot be used. The key difficulties of the thermoelectric performance measurement for nanowire array materials include two aspects: 1) How to heat the two sides of the specimen uniformly and keep the temperature difference constantly at the same time; 2) How to measure the temperature of the two sides of the specimen with the thickness of 10 to several tens micrometers. A new type heating and temperature measuring technology has been used, and it can be simply described as liquid heating and separate temperature measurement. According to this principle, a thermoelectric performance measurement system has been established.

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。

Bi_(2)Te_(3)/KOH/PEDOT:PSS和SiO_(2)气凝胶增强钢丝绒热电性能研究

在热电材料研究领域,一般认为金属的Seebeck系数较低,因此有关金属的热电性能的研究并不多见。但研究发现金属的物理形态对其热电性能具有影响。考察了金属纤维钢丝绒(SW)的热电性能。发现SW(主要成分为Fe)的Seebeck系数是块体铁的2倍。在此基础上,将SW与有机和无机热电材料进行复合,并在其空隙中填充SiO_(2)气凝胶,最终制备出了Bi_(2)Te_(3)/KOH/PEDOT:PSS@SW-SiO_(2)气凝胶复合材料,使其热电性能得到了进一步提升。结果表明,气凝胶的加入可使SW的导热系数降低34%。电导率(σ)、热导率(κ)和Seebeck系数(S)得到解耦。Bi_(2)Te_(3)/KOH/PEDOT:PSS@SW-SiO_(2)气凝胶的Seebeck系数、热电优值(ZT)和功率因子(PF)分别是纯SW的1.2、3.4、2.4倍。通过改变材料物理形态和添加气凝胶来提高材料热电性能的方式有望为其他热电材料的研究提供新的思路和有益参考。

Bi_(2)Te_(3)基热电材料输运性质优化策略研究进展

随着能源需求的持续增长和不可再生资源的不断耗竭,世界各国高度关注新型能源的开发,同时也致力于提高工业废热的回收率和利用率。热电材料是一种能够实现热能和电能直接转换的固态介质,以其为核心的热电器件不含运动附件且不排放污染物,已在半导体制冷和局部热管理领域实现商业化,例如户外制冷机、车载冷柜、光电芯片和功率激光器的控温装置等。热电制冷非常适于小空间热源的主动冷却,可能成为下一代通讯和信息技术的热管理难题中唯一可行的解决方案。Bi_(2)Te_(3)基化合物作为近室温区兼具稳定理化性质和优异输运性质的热电材料,一直受到学术界和产业界的广泛关注。本文在概述热电材料研究背景和制备方法的基础上,从能带工程、声子散射工程、热变形工艺、结构低维化等方面对热电性能的优化方法进行了归纳,并对未来机遇进行了展望。

Thermodynamic Performance of Three-Terminal Hybrid Quantum Dot Thermoelectric Devices

We propose four different models of three-terminal quantum dot thermoelectric devices. From general thermodynamic laws, we examine the rew;rsible efficiencies of the four different models. Based on the master equation, the expressions for the efficiency and power output are derived and the corresponding working regions are determined. Moreover, we particularly analyze the performance of a three-terminal hybrid quantum dot refrigerator. The performance characteristic curves and the optimal performance parameters are obtained. Finally, we discuss the influence of the nonradiative effects on the optimal performance parameters in detail.

Donor-acceptor conjugated copolymer with high thermoelectric performance:A case study of the oxidation process within chemical doping

The doping process and thermoelectric properties of donor-acceptor(D-A)type copolymers are investigated with the representative poly([2,6-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene]3-fluoro-2-[(2-ethylhexyl)-carbonyl]thieno[3,4-b]thiophenediyl))(PTB7-Th).The PTB7-Th is doped by Fe Cl;and only polarons are induced in its doped films.The results reveal that the electron-rich donor units within PTB7-Th lose electrons preferentially at the initial stage of the oxidation and then the acceptor units begin to be oxidized at a high doping concentration.The energy levels of polarons and the Fermi level of the doped PTB7-Th remain almost unchange with different doping levels.However,the morphology of the PTB7-Th films could be deteriorated as the doping levels are improved,which is one of the main reasons for the decrease of electrical conductivity at the later stage of doping.The best electrical conductivity and power factor are obtained to be 42.3 S·cm^(-1);and 33.9μW·mK^(-1),respectively,in the doped PTB7-Th film at room temperature.The power factor is further improved to 38.3μW·mK^(-1);at 75℃.This work may provide meaningful experience for development of D-A type thermoelectric copolymers and may further improve the doping efficiency.

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.

Fabrication and performance evaluation of the thermoelectric generation and performance measuring system

A novel thennoelectric generating and performance measuring system （TGPMS） was designed and fabricated. TGPMS can not only achieve the function of thennoelectric generation, but also measure the thennoelectric performance parameters of the bismuth-telluride-based thennoelectric device accurately. These thennoelectric performance parameters mainly include the dependence of the Seebeck coefficient of the thennoelectric device on the device＇s temperature in the low temperature range （about 40 ~ 190~C ）, and the dependence of the power output and thermoelectric conversion efficiency on the temperature dif- ference or output load. With the optimum load, the optimal value of the power output is 3.39W when the temperature difference reaches 231.2~C, and the optimal value of the conversion efficiency is 3.22% when the temperature difference reaches 208.9~C. TGPMS provides an experimental foundation for the application of the thennoelectric generators in the space field.

Predicted High Thermoelectric Performance of Quasi-Two-Dimensional Compound GeAs Using First-Principles Calculations

The electronic structure of binary quasi-two-dimensional GeAs is investigated using first-principles calculations, and it is found that the anisotropic structure of the layered compound GeAs brings about the anisotropy of the transport properties. Meanwhile, the band structure of GeAs exhibits a relatively large dispersion near the valence-band maximum in the Z –V direction while it is rather flat in the Z –Γ direction, which is highly desirable for good thermoelectric performance. The calculated partial charge density distribution also reveals that GeAs possesses anisotropic electrical conductivity. Based on the semi-classical Boltzmann transport theory, the anisotropic transport properties are observed, and the optimal doping concentrations are estimated. The temperature dependence transport properties of p-type GeAs are compared with the experimental data in good agreement, and the theoretical figure-of-merit ZT has been predicted as well.

Optimal Performance Analysis of a Three-Terminal Thermoelectric Refrigerator with Ideal Tunneling Quantum Dots

The model of a three-terminal thermoelectric refrigerator with ideal tunneling quantum dots is established. It consists of a cavity connected to two quantum dots embedded between two electron reservoirs at different temperatures and chemical potentials. According to the Landauer formula the expressions for the heat current, the cooling rate and the coefficient of performance （COP） are derived analytically. The performance characteristic curves of the cooling rate versus the coefficient of performance are plotted with numerical calculation. The optimal regions of the cooling rate and the COP are determined. Moreover, we optimize the cooling rate and the COP with respect to the position of energy level of the right quantum dot, respectively. The influence of the width of energy level and the temperature ratio on performance of the three-terminal thermoelectric refrigerator is analyzed. Lastly, when the width of energy level is small enough, the optimal performance of the refrigerator is discussed in detail.

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.

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%。

Clathrate structure of YB_(3)C_(3) for high-performance thermoelectrics with superior mechanical properties

Exploring high-performance thermoelectric materials with improved mechanical properties is important for broadening the application scope and the assembly requirement of stable devices.This work presents an effective strategy to discover hard thermoelectric material by inserting foreign atoms in the rigid covalent framework.We demonstrate this in boron-carbon clathrate VII structure,showing a promising candidate for highly efficient thermoelectric energy conversion,especially with Y atom filled in the cage,with a peak zT of 0.73 at 1,000 K.The ab initio calculations indicate that YB_(3)C_(3) system has low lattice thermal conductivity of 4.5 W/(m·K)at 1,000 K due to the strong rattling of encaged Y atom.The strongly covalent framework provides highly degenerate band structures consisting of heavy and light electron pockets,which can maintain high carrier mobility arising from small effective mass and thus large group velocity.Consequently,high power factor can be achieved in YB_(3)C_(3) for both electron and hole doping.In addition,it exhibits well mechanical properties and a Vickers hardness of 23.7 GPa because of the strong covalent boron-carbon framework.This work provides a novel avenue for the search of high-performance thermoelectric materials with excellent mechanical properties,based on boron-carbon clathrate structure.