Thermoelectric Properties of Zintl Compound YbZn<Subscript>2</Subscript>Sb<Subscript>2</Subscript> with Mn Substitution in Anionic Framework

The thermoelectric properties of the Zintl compound YbZn₂Sb₂ with isoelectronic substitution of Zn by Mn in the anionic (Zn₂Sb₂)²⁻ framework have been studied. The p-type YbZn_2−x Mn _x Sb₂ (0.0 ≤ x ≤ 0.4) samples were prepared via melting followed by annealing and hot-pressing. Thermoelectric property measurement showed that the Mn substitution effectively lowered the thermal conductivity for all the samples, while it significantly increased the Seebeck coefficient for x < 0.2. As a result, a dimensionless figure of merit ZT of approximately 0.61 to 0.65 was attained at 726 K for x = 0.05 to 0.15, compared with the ZT of ~0.48 in the unsubstituted YbZn₂Sb₂.     

Addressing the Challenges of Commercializing New Thermoelectric Materials

The time it takes for new thermoelectric materials to make the transition from first announcement in peer-reviewed publications to commercialization is undesirably long. As a result, universities, laboratories, government agencies, commercial users, and venture funding providers throughout the world have not supported research in the field to the level that would be expected for such an otherwise promising technology. This delay also has led to some misdirection of research efforts and a lack of availability of dependable long-term sponsorship commitments to research in the field. From the perspective of commercial users, this presentation discusses the challenges that the thermoelectric material research community faces in creating materials of commercial value. These challenges are broken down into objectives for both the traditional research activities related to improving ZT and those efforts needed to satisfy other, less recognized requirements which, if unaddressed, can significantly impede or even prevent commercialization. The ZT thresholds that enable much larger markets are presented for power generation, cooling, heating, and temperature control materials. Other important considerations, including semiconductor to metal interface (metallization) properties, material stability and constituent requirements, and costs and environmental-impact-related requirements are discussed. At the system level, factors that impede material development are identified, including challenges arising from a lack of property measurement repeatability among different organizations. Approaches and results are compared with that of the more heavily funded and rapidly developing photovoltaic field. The presentation concludes with recommendations for measures to accelerate thermoelectric material commercialization. International Conference on Thermoelectrics (August 3–7, 2008, Corvallis, Oregon, USA).     

Zintl结构化学在热电材料研究中的应用

Zintl相化合物满足“电子晶体-声子玻璃”特征,能够通过化学掺杂和结构修饰来提高其热电性能,是理想的热电材料研究对象。阐明了热电材料性能优化的Zintl结构化学原理,介绍了Zintl结构化学在高性能热电材料研究中的应用,指出利用Zintl结构化学原理寻找高性能热电材料是今后热电材料研究的重要方向。     

Thermoelectric Properties of Zn-Substituted Magnetite

Thermoelectric properties of Zn-substituted magnetite were investigated experimentally. Since Zn is incorporated in the A-site of magnetite for 0 ≤ x ≤ 0.2 in Zn _x Fe_3−x O_4−δ , electrical resistivity remained constant in this region and the thermoelectric power factor (PF) increased with Zn content. At x = 0.2, it attained 1.66 μW/K² cm at 700°C. Above x = 0.2, where Zn began to enter the B-site, the PF decreased with x.     

Thermal stability of melt grown Tl-doped PbTeSe material for thermoelectric applications

Although the thermoelectric performance of PbTe-based materials, processed by hot-pressing, has recently been improved, there are concerns about its thermal stability. On the other hand, during the process of melt crystal growth the material is formed in a quasi-equilibrium condition, which results in homogeneous solid structure in a lower-energy state and, consequently, more thermally stable and mechanically robust. To test the thermal stability of the melt-grown crystal, a Tl-doped PbTe_0.85 Se_0.15 ingot has been grown from the melt by directional solidification. Four adjacent disc-shape samples were sliced perpendicular to the growth axis from the grown boule. The thermoelectric characterizations together with microstructure examination and mechanical hardness measurements were performed on each of the three as-grown samples as well as on the fourth sample after it has been annealed at 455 °C for 570 h. The characterization results, showing that the annealing has essentially no effects on the thermoelectric properties, metallurgical microstructure as well as mechanical hardness of the annealed sample, have demonstrated that structurally homogeneous materials processed by melt growth are more suitable than those processed by other methods, such as hot press or quench-annealing, for long-term thermoelectric applications at elevated temperatures.     

Automotive Applications of Thermoelectric Materials

This report reviews several existing and potential automotive applications of thermoelectric technology. Material and device issues related to automotive applications are discussed. Challenges for automotive thermoelectric applications are highlighted.     

High-pressure preparation and thermoelectric properties of Bi0.85Sb0.15

Nanocrystalline Bi_0.85Sb_0.15 powders were prepared by a novel mechanical alloying method. The bulk samples were formed by applying a pressure of 6 GPa at different pressing temperatures and times. Electrical conductivity, Seebeck coefficients, and thermal conductivity were measured in the temperature range 80–300 K. The Seebeck coefficient reaches a maximum value of −173 μV/K at 150 K. The largest figure of merit, 3.46 × 10⁻³ K⁻¹, achieved in this experiment is 50% higher than that of its single-crystal counterpart at 200 K.     

Solid and soft nanostructured materials: Fundamentals and applications

The scientific work worldwide on nanostructured materials is extensive as well as the work on the applications of nanostructured materials. We will review quasi two-, one- and zero-dimensional solid and soft materials and their applications. We will restrict ourselves to a few examples from partly fundamental aspects and partly from application aspects. We will start with trapping of excitons in semiconductor nanostructures. The subjects are: physical realizations, phase diagrams, traps, local density approximations, and mesoscopic condensates. From these fundamental questions in solid nanomaterials we will move to trapping of molecules in water using nanostructured electrodes. We will also discuss how to manipulate water (create vortices) by nanostructure materials.The second part deals with nanorods (nano-wires). Particularly we will exemplify with ZnO nanorods. The reason for this is that ZnO has: a very strong excitons binding energy (60 meV) and strong photon-excitons coupling energy, a strong tendency to create nanostructures, and properties which make the material of interest for both optoelectronics and for medical applications. We start with the growth of crystalline ZnO nanorods on different substrates, both crystalline (silicon, silicon carbide, sapphire, etc) and amorphous substrates (silicon dioxide, plastic materials, etc) for temperatures from 50 °C up to 900 °C. The optical properties and crystalline properties of the nanorods will be analyzed. Applications from optoelectronics (lasers, LEDs, lamps, and detectors) are analyzed and also medical applications like photodynamic cancer therapy are taken up.The third part deals with nano-particles in ZnO for sun screening. Skin cancer due to the exposure from the sun can be prevented by ZnO particles in a paste put on the exposed skin.     

Thermoelectric Properties of Heavily Doped <Emphasis Type="Italic">n</Emphasis>-Type SrTiO<Subscript>3</Subscript> Bulk Materials

Three Ta-doped strontium titanates were prepared as potential candidates for n-type thermoelectric oxides. The purity of the polycrystalline samples of SrTi_1−x Ta _x O₃ (x = 0.05 to 0.14) were characterized by means of powder x-ray diffraction and electron probe micro analysis (EPMA). We present the results of Seebeck coefficient, electrical conductivity, and thermal conductivity measurements performed at high temperatures.     

半导体制冷中的饱和电流

对半导体制冷中的论和电流现象进行了解释。理论分析表明，要使器件在△Tmax条件下工作，对元件高度应有一定限制。