▪ Abstract Recently there has been a resurgence of research efforts related to the investigation of new and novel materials for small-scale thermoelectric refrigeration and power generation applications. These materials need to couple and optimize a variety of properties in order to exhibit the necessary figure of merit, i.e. the numerical expression that is commonly used to compare one potential thermoelectric material with another. The figure of merit is related to the coefficient of performance or efficiency of a particular device made from a material. The best thermoelectric material should possess thermal properties similar to that of a glass and electrical properties similar to that of a perfect single-crystal material, i.e. a poor thermal conductor and a good electrical conductor. Skutterudites are materials that appear to have the potential to fulfill such criteria. These materials exhibit many types of interesting properties. For example, skutterudites are members of a family of compounds we call...

SKUTTERUDITES : A phonon-glass-electron crystal approach to advanced thermoelectric energy conversion applications

Filled skutterudites R_xCo_4Sb_(12) are excellent n-type thermoelectric materials owing to their high electronic mobility and high effective mass, combined with low thermal conductivity associated with the addition of filler atoms into the void site. The favourable electronic band structure in n-type CoSb3 is typically attributed to threefold degeneracy at the conduction band minimum accompanied by linear band behaviour at higher carrier concentrations, which is thought to be related to the increase in effective mass as the doping level increases. Using combined experimental and computational studies, we show instead that a secondary conduction band with 12 conducting carrier pockets (which converges with the primary band at high temperatures) is responsible for the extraordinary thermoelectric performance of n-type CoSb_3 skutterudites. A theoretical explanation is also provided as to why the linear (or Kane-type) band feature is not beneficial for thermoelectrics.

Convergence of multi-valley bands as the electronic origin of high thermoelectric performance in CoSb3 skutterudites.

A review on the enhancement of figure of merit from bulk to nano-thermoelectric materials

Recent progress of half-Heusler for moderate temperature thermoelectric applications

This paper reviews the development of energy harvesting for low-power embedded structural health monitoring (SHM) sensing systems. A statistical pattern recognition paradigm for SHM is first presented and the concept of energy harvesting for embedded sensing systems is addressed with respect to the data acquisition portion of this paradigm. Next, various existing and emerging sensing modalities used for SHM and their respective power requirements are summarized followed by a discussion of SHM sensor network paradigms, power requirements for these networks, and power optimization strategies. Various approaches to energy harvesting and energy storage are discussed and limitations associated with the current technology are addressed. The paper concludes by defining some future research directions that are aimed at transitioning the concept of energy harvesting for embedded SHM sensing systems from laboratory research to field-deployed engineering prototypes. Finally, it is noted that many of the technologies discussed herein are applicable to powering any type of low-power embedded sensing system regardless of the application.

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Energy Harvesting for Structural Health Monitoring Sensor Networks

Effects of doping on the transport properties of CoSb3 have been systematically investigated using Ni, Pd, and Pt as donor impurities. It is shown that the Hall mobility, the Seebeck coefficient, and the electrical conductivity depend strongly not only on the carrier concentration but also on these donor impurities. Our theoretical analysis suggests that the electron effective mass and the conduction band deformation potential are significantly affected by both the doping levels and the donor impurities. These doping effects in CoSb3 can be attributed to (1) the changes in the electronic structure with doping and (2) the specific nature of the conduction band structure, in particular, the nonparabolicity of the band which can be explained in terms of a two-band Kane model. The observed changes in the electronic properties with doping are also consistent with the predictions of a recent band structure calculation of CoSb3. On the other hand, the lattice thermal conductivity decreases markedly with increasi...

Effects of doping on the transport properties of CoSb3

The development of a high efficiency thermoelectric (TE) stack, which is a united system of thermoelectric modules and a heat exchanger, has been made to advance the applications of electrical power generation to vehicles. The thermoelectric materials under investigation are mostly heavily doped CoSb/sub 3/ and filled skutterudites RM/sub 4/Sb/sub 12/ (R= Ce, Yb,; M=Co, Fe, Ni, Pt, Pd). In order to maximize the conversion efficiency of the devices operating in the 350-750/spl deg/C temperature range, the p-, n-legs segmented with the skutterudites and state-of-the-art Bi/sub 2/Te/sub 3/ have been used to build the devices. We could obtain valuable data showing a validity of installing the thermoelectric stack in vehicles, but a few of problems to be solved in a practical level still remain.

Development of a high efficient thermoelectric stack for a waste exhaust heat recovery of vehicles

The structural and electronic transport properties of polycrystalline p-type CoSb3 with different grain sizes (about 3 and 3×102 μm) were investigated. The magnetic susceptibility was also measured. Samples were characterized by x-ray diffractometry, electron-probe microanalysis, and optical microscope observation. Samples were found to be stoichiometric and homogeneous. The Hall carrier concentration of the samples is of the order of 1018 cm−3 and weakly dependent on the temperature. The temperature dependence of the Hall mobility suggests that the predominant scattering mechanism drastically changes depending on grain size: for large grain size a combination of the neutral impurity scattering and the acoustic phonon scattering, and for small grain size the ionized impurity scattering. The magnetic susceptibility was found to be essentially diamagnetic independently of grain size, and to vary slightly with temperature. The weak temperature dependence of the susceptibility can be explained by taking into account the three contributions of ion cores, conduction electrons, and trace amounts of magnetic impurities. From the analysis of the susceptibility due to conduction electrons, the band gap energy was determined to be about 70–80 meV, consistent with a recent band structure calculation. Although the effects of nonmagnetic impurity phases segregated (Sb, etc.) on the scattering mechanism are not clear, the grain size is one of the key factors determining the transport properties of polycrystalline CoSb3.

Structural and electronic transport properties of polycrystalline p-type CoSb3

We present some results on physical and electrical properties of the Skutterudites CoSb/sub 3/ and mixed alloys. Most of samples measured were polycrystalline, which have been prepared by hot-pressing of powders under 10/sup 7/ Pa at /spl sim/650/spl deg/C and /spl sim/750/spl deg/C, and a few measurements on CoSb/sub 3/ single crystals were performed. We report some results of the Hall mobility, Seebeck coefficient and electrical conductivity measurements on CoSb/sub 3/ and mixed alloys. Based on the experimental results, we make clear important factors which have influence on the electronic transport properties, in particular, on the Hall mobility of the materials.

Electronic transport properties of the Skutterudite CoSb 3 and mixed alloys

Electron tunneling experiments were performed on p-Co1−xFexSb3–Al-oxide–Al junctions for x=0 and x=01 at 42 K A U-shaped tunneling conductance curve obtained for polycrystalline p-CoSb3 clearly shows an energy-band gap of ∼50 meV For p-Co09Fe01Sb3 skutterudites, a strong zero-bias conductance anomaly is observed This anomaly may be due to a structural disorder arising from defects such as vacancies and interstitial Fe atoms

K. Matsubara

Papers

Effects of doping on the transport properties of CoSb3

Development of a high efficient thermoelectric stack for a waste exhaust heat recovery of vehicles

Structural and electronic transport properties of polycrystalline p-type CoSb3

Electronic transport properties of the Skutterudite CoSb 3 and mixed alloys

Electron tunneling experiments on skutterudite Co1−xFexSb3 semiconductors