SnSe exhibits exceptionally high thermoelectric (TE) figure of merit zT mainly due to its ultralow lattice thermal conductivity (¬ lat) [L.-D. Zhao et al.: Nature 508 (2014) 373.]. It is considered that strong lattice anharmonicity caused by the lone pair electrons of Sn 2+ results in the ultralow ¬ lat. Here, we focus on SnO because it has the lone pair electrons of Sn 2+ like SnSe. Bulk samples of SnO were synthesized by low-temperature high-pressure spark plasma sintering and their TE properties were examined. The present study revealed that SnO exhibits very low ¬ lat (1.44 Wm ¹1 K ¹1 at 573 K) compared with SnO 2 which has no lone pair electrons. The Grüneisen parameter (£) of SnO was evaluated to be 1.70 and this high £ leads to large lattice anharmonicity and thereby low ¬ lat. Even though SnO has low ¬ lat , the zT values were significantly low compared with SnSe. The maximum zT value of SnO was 0.00141 at 573 K. Since the main reason of this low zT is its non-optimized carrier concentration, the zT of SnO can be enhanced through the carrier concentration optimization.

Corresponding author: email psupree@kk.ac.th, Phone: þ66 87 373 11 22, Fax: þ66 43 203 359 In this research, the p-type Si 80 Ge 20 B 3 alloys composited with YSi 2 nanoinclusions were fabricated by melting spinning and then, spark plasma sintering. The metallic Y was chosen as the source of YSi 2 nanoparticles. It was found that the fully dense nanocomposites were formed with the homogeneous distribution of YSi 2 nanoinclusions in the SiGe matrix. The thermoelectric measurement showed that YSi 2 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.

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.

Metal silicide-based thermoelectric (TE) materials have attracted attention owing to low toxicity and high chemical stability. Here, we demonstrate that ytterbium silicon-germanium, Yb(Si1−xGex)2−δ, shows a large Seebeck coefficient (S) accompanied by metal-like high electrical conductivity (σ) attributed to the intermediate valence behavior of Yb (Yb2+/Yb3+). We revealed that x = 0.5, i.e., YbSiGe, is the best composition with the highest power factor (S2σ) of 3.6 mW m−1 K−2 at room temperature, which is comparable to those of conventional TE materials, such as Bi2Te3.

PbTe systems are known as good thermoelectric materials for midtemperature range applications. Here, we demonstrate that a method of melt-spinning followed by pulsed electric current sintering is effective to synthesize nanostructured bulk PbTe with enhanced thermoelectric properties. The bulk samples with the nominal composition PbTe−2% MgTe doped with 4% Na consist of a hierarchical nanostructure, where MgTe-based nanoprecipitates with the size of ∼2−15 nm exist in the PbTe grains that are several hundred nm in size. Both the nanoscale precipitates and the high-density grain boundaries effectively scatter heat-carrying phonons, leading to significant reduction in the lattice thermal conductivity. Furthermore, an increased Seebeck coefficient is observed, which can be explained by band convergence induced by alloying Mg and energy filtering induced by grain boundaries. The simultaneous realization of the decreased lattice thermal conductivity and increased Seebeck coefficient results in the enhanced thermoelectric figure of merit zT to be around 1.3 at 753 K.

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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− xGe x)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 4 f 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.

Nanostructured bulk silicon (bulk nano-Si) has attracted attention as an advanced thermoelectric (TE) material due to its abundance and low toxicity.