In the present study, we investigated the high-temperature thermoelectric (TE) properties of AgGaTe2 with chalcopyrite structure. We tried to enhance the TE properties of AgGaTe2 by reducing the Ag content. The reduction of Ag increased the carrier concentration, leading to enhancement of the dimensionless figure of merit (ZT). The maximum ZT value was 0.77 at 850 K obtained in Ag0.95GaTe2, which was approximately two times higher than that of stoichiometric AgGaTe2.

In recent years, nanostructured thermoelectric materials have attracted much attention. However, despite this increasing attention, available information on the thermoelectric properties of single-crystal Si is quite limited, especially for high doping concentrations at high temperatures. In this study, the thermoelectric properties of heavily doped (10 18 -10 20 cm %3 ) n-and p-type single-crystal Si were studied from room temperature to above 1000 K. The figures of merit, ZT, were calculated from the measured data of electrical conductivity, Seebeck coefficient, and thermal conductivity. The maximum ZT values were 0.015 for n-type and 0.008 for p-type Si at room temperature. To better understand the carrier and phonon transport and to predict the thermoelectric properties of Si, we have developed a simple theoretical model based on the Boltzmann transport equation with the relaxation-time approximation.

The effectiveness of thermoelectric (TE) materials is quantified by the dimensionless figure of merit (zT). An ideal way to enhance zT is by scattering phonons without scattering electrons. Here we show that, using a simple bottom-up method, we can prepare bulk nanostructured Si that exhibits an exceptionally high zT of 0.6 at 1050 K, at least three times higher than that of the optimized bulk Si. The nanoscale precipitates in this material connected coherently or semi-coherently with the Si matrix, effectively scattering heat-carrying phonons without significantly influencing the material's electron transport properties, leading to the high zT.

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In this study, the temperature-dependent thermoelectric properties of p-type single-crystal Ge, which is a useful material for thermoelectric applications owing to its significantly high carrier mobility, were investigated. The thermoelectric properties of Ga-doped (5.7 ' 10 16 , 3.4 ' 10 18 , and 1.0 ' 10 19 cm %3 ) p-type single-crystal Ge were measured from room temperature to 770 K. The sample with a carrier concentration of 1.0 ' 10 19 cm %3 showed the highest thermoelectric figure of merit, ZT, over the entire measured temperature range. The maximum ZT value was 0.06 at 650 K. A theoretical model based on the Boltzmann transport equation with relaxation-time approximation was developed and quantitatively reproduced the experimentally observed data. The optimal impurity concentration predicted by this model was 3 ' 10 19 cm %3 at 300 K and increased with temperature.

The effectiveness of thermoelectric (TE) materials at converting heat gradients into electricity, and vice versa, is quantified by the dimensionless figure of merit, ZT. Current TE materials, such as Bi 2 Te 3 and PbTe, have ZT values of approximately 1, but contain highly toxic and/or rare elements, which limits their widespread use. However, Si is a non-toxic, inexpensive, and abundant element. Even though bulk Si exhibits good electrical properties, its lattice thermal conductivity (¬ lat ) is high (>100 Wm ¹1 K ¹1), which results in a ZT value of approximately 0.01 at room temperature. If it were possible to lower the ¬ lat of Si without altering the electrical properties, Si would be an ideal TE material. These changes can be realized by nanostructuring Si. In this review, we discuss the recent achievements in the enhancement of the TE properties of Si via nanostructuring. Based on these recent results, we also indicate some potential topics to investigate to enhance the TE properties of Si further.

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CuGaTe 2 has recently been reported to have a high thermoelectric (TE) figure of merit (Z T ) of 1.4 at 950 K [T. Plirdpring et al.: Adv. Mater. 24 (2012) 3622]. However, the Z T values of CuGaTe 2 in the low and middle temperature ranges are not high, due to high lattice thermal conductivity ( lat ) in those temperature ranges. We have attempted to reduce the lat of CuGaTe 2 by the substituting Ag into the Cu sites. Polycrystalline samples of Cu 1Àx Ag x GaTe 2 (x ¼ 0, 0.25, 0.5, 0.75, and 1) were prepared and the TE properties were examined. Ag substituted reduced lat and changed the carrier concentration and mobility, which improved Z T in the low and middle temperature ranges; a Z T value of 0.7 was obtained at 700 K for Cu 1Àx Ag x GaTe 2 with x ¼ 0:5, which is 40% higher than that of CuGaTe 2 . #