Complex thermoelectric materials

Thermoelectric materials, which can generate electricity from waste heat or be used as solid-state Peltier coolers, could play an important role in a global sustainable energy solution. Such a development is contingent on identifying materials with higher thermoelectric efficiency than available at present, which is a challenge owing to the conflicting combination of material traits that are required. Nevertheless, because of modern synthesis and characterization techniques, particularly for nanoscale materials, a new era of complex thermoelectric materials is approaching. We review recent advances in the field, highlighting the strategies used to improve the thermopower and reduce the thermal conductivity.     

Recent advances in thermoelectric materials

Thermoelectric materials are crucial in renewable energy conversion technologies to solve the global energy crisis. They have been proven to be suitable for high-end technological applications such as missiles and spacecraft. The thermoelectric performance of devices depends primarily on the type of materials used and their properties such as their Seebeck coefficient, electrical conductivity, thermal conductivity, and thermal stability. Classic inorganic materials have become important due to their enhanced thermoelectric responses compared with organic materials. In this review, we focus on the physical and chemical properties of various thermoelectric materials. Newly emerging materials such as carbon nanomaterials, electronically conducting polymers, and their nanocomposites are also briefly discussed. Strategies for improving the thermoelectric performance of materials are proposed, along with an insight into semiconductor physics. Approaches such as nanostructuring, nanocomposites, and doping are found to enhance thermoelectric responses by simultaneously tuning various properties within a material. A recent trend in thermoelectric research shows that high-performance thermoelectric materials such as inorganic materials and carbon nanomaterials/electronically conducting polymer nanocomposites may be suitable for power generation and energy sustainability in the near future.     

超晶格热电材料研究进展

本文讨论了超晶格材料在热电方面的应用以及超晶格提高材料热电性能的原因和存在的问题,并介绍了几种超晶格热电材料研究情况。     

Ca(Na)-Co-O基热电氧化物研究进展

介绍了钴基氧化物热电材料研究现状及前景.重点介绍了具有潜力的Na/Ca-Co-O热电氧化物材料的结构、热电性能特征、制备等研究现状;并对Na/Ca-Co-O基热电氧化物Na/Ca位和Co位掺杂研究进行了评述;最后指出了钴基氧化物热电材料的应用前景和研究方向.     

Extruded materials for thermoelectric coolers

We have optimized the compositions of p-type thermoelectric materials based on solid solutions between bismuth and antimony tellurides with high thermoelectric figures of merit in different temperature ranges between 100 and 300 K. The materials have been prepared by extrusion and have been characterized by microstructural analysis. Their thermoelectric properties have been studied in the range 100–400 K.     

Routes for high-performance thermoelectric materials

Thermoelectric materials can be used in direct conversion of heat to electricity and vice versa. The past decade has witnessed the rapid growth of thermoelectric research, targeting high thermoelectric performance either via reduction in the lattice thermal conductivity or via enhancement of the power factor. In this review, we firstly summarize the recent advances in bulk thermoelectric materials with reduced lattice thermal conductivity by nano-microstructure control and also newly discovered materials with intrinsically low lattice thermal conductivity. We then discuss ways to enhance the electron transport abilities for achieving higher power factor by both novel and traditional methods. Finally, we highlight the recent development in single-crystal thermoelectric materials. These strategies are successful in synergistically manipulating the thermal conductivity and electron transport properties, which have significantly advanced thermoelectric performance on materials. For device applications on these high-performance materials, new opportunities may arise though stability, electrode contacts, mechanical properties, and other problems need to be solved in the near future.     

热电材料新进展

本文评述了热电材料研究的最新发展,指出它在制冷技术和能源工程上的广阔应用前景,系统地分析了影响品质因子提高的各种因素,指出了提高品质因子的一些可能途径。     

氧化物热电材料的研究进展

介绍了氧化物热电材料的研究现状及发展趋势,以及氧化物热电材料的特殊优点;同时对氧化物热电材料做了大致分类.深入介绍了关于错配层氧化物高热电势起因的最新研究成果;广泛介绍了perovskite结构氧化物的置换对热电性能的影响,探讨了其导电机理及热电势的可能起因.最后介绍了透明导电氧化物热电材料.     

Composite thermoelectric materials with embedded nanoparticles

The current status of the development of composite thermoelectric materials with embedded nanoparticles is reviewed. An introduction is given to the suggested mechanisms of improving thermoelectric properties by inclusions of nanoparticles and to experimental methods used to prepare such composites. The progress made in the development of thermoelectric materials with embedded nanoparticles is then covered, grouping the studies according to the optimal temperature range of operation of the materials investigated. Most studies have been devoted to materials within the medium temperature range, followed by low temperature materials, whereas high temperature materials have not yet received much attention within this area. In the majority of the materials systems studied, reports of improved thermoelectric performance upon introduction of nanoparticles in bulk thermoelectrics are found. However, for continued progress in this area, there is a need for systematic experimental studies that unambiguously correlate the resulting physical effects of the nanoinclusions to the measured materials properties.     

Peculiarities of thermophysical measurements of thermoelectric materials

This paper examines a method for direct measurement of the heat losses in determining the thermal conductivity of thermoelectric materials.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 36, No. 5, pp. 891–895, May, 1979.     

Graded carrier concentration materials for thermoelectric coolers

We have optimized the compositions of p-and n-type graded thermoelectric materials based on solid solutions between bismuth and antimony chalcogenides with high thermoelectric efficiency in the temperature range 100–400 K. Czochralski-grown graded single crystals have been used to fabricate graded legs 2.5 mm in height and 1.4 × 1.4 mm² in cross-sectional area for different stages of thermoelectric coolers. Pilot thermoelectric modules have been fabricated using homogeneous and graded legs, and the maximum temperature difference across the modules has been measured from 100 to 300 K. The efficiency of the modules with graded legs is shown to exceed that of the modules with homogeneous legs, especially at low temperatures.     

Heat-flux transducers based on artificially anisotropic thermoelectric materials

The use of artificially anisotropic thermoelectric material as a heat-flux transducer, the method of selecting its components, and optimization of the parameters are discussed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 2, pp. 229–233, August, 1978.     

Tuning phonon transport spectrum for better thermoelectric materials

The figure of merit of thermoelectric materials can be increased by suppressing the lattice thermal conductivity without degrading electrical properties. Phonons are the carriers for lattice thermal conduction, and their transport can be impeded by nanostructuring, owing to the recent progress in nanotechnology. The key question for further improvement of thermoelectric materials is how to realize ultimate structure with minimum lattice thermal conductivity. From spectral viewpoint, this means to impede transport of phonons in the entire spectral domain with noticeable contribution to lattice thermal conductivity that ranges in general from subterahertz to tens of terahertz in frequency. To this end, it is essential to know how the phonon transport varies with the length scale, morphology, and composition of nanostructures, and how effects of different nanostructures can be mutually adopted in view of the spectral domain. Here we review recent advances in analyzing such spectral impedance of phonon transport on the basis of various effects including alloy scattering, boundary scattering, and particle resonance.     

Crystal microstructure suitable for high-performance thermoelectric bulk materials

The resultant thermoelectric power factor P and figure of merit Z of two types of composite device composed of a sandwich structure (A/B/A) were calculated by treating these devices electrical and thermal circuits. When the direction of the temperature gradient is perpendicular to a sandwiched slab with a lower ρ and a higher κ than those of the dominant material (a) and is parallel to a slab with a higher ρ and a lower κ than those of the dominant material (b), P increased significantly at an optimum slab thickness for device (a), in accordance with the result obtained by Bergman and Fel for a similar composite device, but decreased abruptly with increasing slab thickness for device (b), while Z remained almost unchanged with slab thickness for both devices as long as a thin slab is used. It was clarified that well-known high-performance thermoelectrics have crystal structures or microstructures corresponding to either device (a) or (b) fitted to enhance the boundary effect at the interface. Therefore, it is expected that when a number of thinly layered phases aligned in one direction are introduced into the microstructures of high-performance bulk materials; they enable the significant enhancement of boundary effect alone, resulting in a significant increase in Z of such bulk materials.     

Preparation of thermoelectric materials based on higher manganese silicide

Rhenium-doped higher manganese silicide based materials have been prepared by hot pressing. It has been shown that the pressing temperature of the materials can be lowered by adding titanium as a reductant or by sonication during pressing. The average thermoelectric figure of merit of the materials in the temperature range 600–900 K is Z ≅ 0.7 × 10⁻³ K⁻¹.     

On chessboard buckling modes in compressed materials

The article is concerned with a transversely isotropic homogeneous elastic medium subjected to uniform compression in the isotropy plane. The medium becomes unstable in the sense of Hadamard at a certain level of initial strain. The critical strain is established to be uniquely determined from the system of equations of the equilibrium bifurcation; however, there are many modes of buckling corresponding to this strain. A solution of the system of the bifurcation equations is considered in the form of double periodic functions of the kind sin r ₁ x ₁ sin r ₂ x ₂. The uncertainty in the buckling mode implies that the wave numbers r ₁ and r ₂ remain arbitrary. In order to determine the relationship between the wave numbers, we examine the initial supercritical behavior of the material. Only two types of buckling modes (the shear type and the volume type) are possible. It is established that the buckling mode of the volume type is a chessboard-like one, and the mode of the shear type is not chessboard like. The stability of the supercritical equilibrium state is discussed.     

Bonding and interfacial reaction between Ni foil and n-type PbTe thermoelectric materials for thermoelectric module applications

Integration of next generation thermoelectric materials in thermoelectric modules requires a novel or alternative approach for mating the brittle semiconducting thermoelectric materials and the ductile metal interconnects. In this study, pure Ni foil was directly bonded to PbTe-based thermoelectric materials using a rapid hot-press. The materials were sintered at 600 and 650 °C, under a pressure of 40 MPa and for various holding times. The resulting interfacial microstructures of the Ni/PbTe joints were investigated. Additionally, the distributions of elements and the phases formed at the Ni/PbTe interface were analyzed. The β₂ phase (Ni_3±x Te₂, 38.8–41 at.% Te) was identified at the Ni/PbTe joints bonded at both 600 and 650 °C. A ternary phase with approximate composition Ni₅Pb₂Te₃ was found at the Ni/PbTe joints bonded at 650 °C. Additionally, the PbTe(Ni) phase was observed along the Ni grain boundaries for both bonding temperatures. Thermodynamics calculation results indicate that only the β₂ phase can be formed at the Ni/PbTe interface at 900 K among the binary nickel tellurides.     

Ⅰ-型锗基笼形物--极有希望的热电材料

对I-型锗基笼形物的制备、晶体结构特别是热电性能等研究现状做了综述。I-型锗基笼形物半导体是具有“声子玻璃、电子晶体”特性的热电材料。它具有笼子状的晶体结构,这种独特的框架结构决定了其具有良好的电性能,而通过填充合适的碱土金属或稀土金属原子到其笼子状的空隙中则可以大大降低体系的热导率,因而是很具希望的热电材料体系。要进一步提高该体系的热电性能,必须在优化填充原子的同时优化框架原子。