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Ytterbium silicide-based thermoelectric materials have attracted attention because they exhibit large power factors owing to large absolute values of their Seebeck coefficient as well as high electrical conductivity. Here, we demonstrate that, in the Yb(Si1−xGex)2 system, by controlling the valence fluctuation, we combine two phenomena, namely, the Kondo effect and suppression of the spin fluctuation. This leads to a large density of states and the suppression of the spin fluctuation of the 4f electrons, thereby resulting in a high Seebeck coefficient with extremely low resistivity. Consequently, Yb(Si0.5Ge0.5)2 exhibits a high-power factor of 8.4 mW K−2 m−1, which makes energy harvesting from a cold source a practical possibility. [ABSTRACT FROM AUTHOR]

Sr(1–x)LaxTiO3 (SLTO) nanopowder (x = 0, 0.01, 0.05, 0.07, and 0.10) were effectively synthesised by the sol-gel auto-combustion process. Bulk ceramics samples were produced by spark plasma sintering (SPS) in an Ar atmosphere. The XRD pattern of the undoped SLTO nanopowder showed the pure phase and the impurity phase (TiO2) was detected in the La-doped SLTO samples. However, the impurity phase disappeared after producing the bulk samples with the SPS process. All the samples exhibited a negative Seebeck coefficient (S). The electrical conductivity (σ) and negative Sof all the SLTO samples increased with increasing temperature and reached a maximum value at 800 K. The thermal conductivity (κ) decreased with increasing temperature and increasing La content. The SLTO with x = 0.01 showed the largest σ, negative S, power factor (S2σ) and dimensionless figure of merit (ZT) at 800 K. [ABSTRACT FROM AUTHOR]

A thermoelectric module is composed of n- and p-type materials, and its performance is evaluated by the materials' dimensionless figure of merit, zT, which is expected to be as high as possible. Moreover, because a thermoelectric module is designed to operate in various temperature ranges, the rate of each material's deformation in response to a change in temperature, also called thermal expansion, should be considered. If n- and p-type materials in a thermoelectric module have a too large difference in the thermal expansion, it could lead to risks of several device failures and reduction in performance over time. Thus, to achieve practical use, not only zT but also the compatibility of n- and p-type materials are also crucial parameters. In this study, we demonstrated a technique used to minimize the difference of thermal expansion rate between n-type Mg2Si and p-type higher manganese silicide, which are the promising materials used for a practical thermoelectric module. [ABSTRACT FROM AUTHOR]

Si-based materials are considered as promising candidates for thermoelectric materials, owing to several advantages such as non-toxicity, abundance, and high stability. One of the strategies to develop high-efficiency Si-based thermoelectric materials with enhanced figure of merit zT is increasing the μH/κlat ratio, where μH and κlat are the Hall mobility and lattice thermal conductivity, respectively. In the present study, we synthesize a bulk Si–Ti nanocomposite composed of Si and Ti silicide by a combined method of melt-spinning and spark plasma sintering and examine the thermoelectric properties. The obtained results are compared with the data for Si–V and Si–Ni nanocomposites reported previously by the authors' group. In the comparison, we focus on (1) size and distribution of the precipitates, (2) the interface between Si and the precipitates, and (3) volume fraction of the precipitates; and investigate the effects of these three factors on keeping high μH and reduction of κlat. Based on the comparison, it is revealed that the uniform distribution of the precipitates and the coherent interface between Si and metal silicide lead to large μH/κlat ratio and thus enhanced zT in the nanocomposites composed of Si and metal silicides. [ABSTRACT FROM AUTHOR]

Mo3Sb7 has been known as a p-type metal with commonly poor thermoelectric properties. However, Mo3Sb7 can be a high-efficiency thermoelectric material, owing to its capability of a metal–semiconductor transition, which can be realized by adding two valence electrons through elemental substitutions. Among the Mo3Sb7-based compounds, Mo3Sb5.4Te1.6 shows the highest figure of merit, zT, but additional valence electrons are needed for further improvement of the figure of merit. Here, we try to enhance the figure of merit of Mo3Sb7 by iodine-doping and by synthesizing and characterizing Mo3Sb7Ix with x = 0, 0.50, 0.75, 1.00, 1.25, and 1.50, where antimony (valence electrons = 5) is replaced by iodine (valence electrons = 7). We confirmed that the solubility limit for iodine in Mo3Sb7Ix was 1.25 < x < 1.50, and the figure of merit was enhanced by approximately 65% in maximum in x = 1.25. [ABSTRACT FROM AUTHOR]

ZrW2O8 is known as a negative coefficient of thermal expansion (CTE) material. In contrast, the studies of other properties than the CTE of ZrW2O8, such as thermal conductivity and mechanical properties, are limited. Herein, a highly dense bulk sample (%T.D. > 95%) of ZrW2O8 from very fine powder (D50 0.3 μm) with a crystalline size of 31 nm using a spark plasma sintering (SPS) technique is synthesized. It is revealed that ZrW2O8 exhibits the lowest level of thermal conductivity among various oxides in a wide temperature range from 300 to 823 K. Furthermore, various physical properties such as a peculiar CTE, elastic constant, and Grüneisen parameter are reported. Owing to its exceptional thermal properties, ZrW2O8 is expected to be used in various thermal management areas. [ABSTRACT FROM AUTHOR]

Flexible thermoelectric (FTE) devices have become attractive in recent years since they can be utilized as a power generator for wearable and portable electronics. This work fabricated FTE nanocomposites from bacterial cellulose (BC) and Ag2Se via an easy and inexpensive method. The blended BC was thoroughly mixed with Ag2Se powders before casting onto a filter paper via vacuum filtration, followed by oven-drying and hot-pressing. Phase formation of Ag2Se in the BC nanofiber network was confirmed by x-ray diffraction and energy dispersive spectroscopy. SEM images revealed the distribution of Ag2Se particles in the BC matrix. The Ag2Se particles were densely packed for large Ag2Se concentrations in the BC/Ag2Se nanocomposite. Thermoelectric measurements found that the electrical conductivity (σ) and Seebeck coefficient (S) varied with the Ag2Se proportion due to the changes in the carrier concentration and carrier mobility. The maximum σ of 5.7 × 104 S/m and S of −80 μV/K were observed at room temperature (RT), yielding the power factor (PF) of ∼300 μW/mK2. This PF value is comparable to other FTE materials, but the process used in this research is much simpler. The thermal conductivity was 0.56 W/mK at RT. Moreover, the BC/Ag2Se nanocomposites were highly flexible and could be attached to curved surfaces. In addition, the FTE module was constructed from BC/Ag2Se uni-leg elements, which could generate an output power of 0.28 μW. In addition, the simple fabrication process makes the BC/Ag2Se nanocomposite readily expandable to an industrial scale for modern FTE devices. [ABSTRACT FROM AUTHOR]

Very recently, it has been reported that Sn(SbTe2)2 exhibits a low κlat (≈0.46 W m−1 K−1 at 720 K), thus making Sn(SbTe2)2 a good thermoelectric material. The low κlat is thought to be due to the anharmonicity of the lattice, but no experimental evidence for this has been reported. Herein, the origin of such low κlat in Sn(SbTe2)2 is experimentally investigated by measuring various physical properties and the linear thermal expansion coefficient. The results show that the Grüneisen parameter of Sn(SbTe2)2 is very high, 3.38, which means that Sn(SbTe2)2 has a large anharmonicity. Due to this large anharmonicity, the Sn(SbTe2)2 sample shows a very low κlat and a relatively high thermoelectric figure of merit zT of 0.32 at 770 K. [ABSTRACT FROM AUTHOR]

Very recently, it has been reported that Sn(SbTe2)2 exhibits a low κlat (≈0.46 W m−1 K−1 at 720 K), thus making Sn(SbTe2)2 a good thermoelectric material. The low κlat is thought to be due to the anharmonicity of the lattice, but no experimental evidence for this has been reported. Herein, the origin of such low κlat in Sn(SbTe2)2 is experimentally investigated by measuring various physical properties and the linear thermal expansion coefficient. The results show that the Grüneisen parameter of Sn(SbTe2)2 is very high, 3.38, which means that Sn(SbTe2)2 has a large anharmonicity. Due to this large anharmonicity, the Sn(SbTe2)2 sample shows a very low κlat and a relatively high thermoelectric figure of merit zT of 0.32 at 770 K. [ABSTRACT FROM AUTHOR]

Metal silicide‐based thermoelectric (TE) materials have attracted attention in the past two decades, because they are less toxic, with low production cost and high chemical stability. Here, we study the TE properties of ytterbium silicide YbSi2 with a specific layered structure and the mixed valence state of Yb2+ and Yb3+. YbSi2 exhibits large Seebeck coefficient, S, accompanied by high electrical conductivity, σ, leading to high power factor, S2σ, of 2.2 mW m−1 K−2 at room temperature, which is comparable to those of state‐of‐the‐art TE materials such as Bi2Te3 and PbTe. Moreover, YbSi2 exhibits high Grüneisen parameter of 1.57, which leads to relatively low lattice thermal conductivity, κlat, of 3.0 W m−1 K−1 at room temperature. The present study reveals that YbSi2 can be a good candidate of TE materials working near room temperature. [ABSTRACT FROM AUTHOR]

In this research, the p-type Si80Ge20B3 alloys composited with YSi2 nanoinclusions were fabricated by melting spinning and then, spark plasma sintering. The metallic Y was chosen as the source of YSi2 nanoparticles. It was found that the fully dense nanocomposites were formed with the homogeneous distribution of YSi2 nanoinclusions in the SiGe matrix. The thermoelectric measurement showed that YSi2 addition reduces the electrical conductivity but increases the Seebeck coefficient, which was attributed to the decrease in carrier concentration. The thermal conductivity was suppressed for the composite SiGe-1.4%Y, which made this composition to exhibit the largest thermoelectric figure-of-merit (ZT) of 0.52. Figure-of-merit (ZT) and microstructure of the SiGe- x%Y SiGe-1.4%Y. [ABSTRACT FROM AUTHOR]