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First, a large sample of Ni0.05Mo3Sb5.4Te1.6 was prepared by heating the elements in the stoichiometric ratio. β-SiC nanoparticles were added in volume fractions, f, of 0.01, 0.02, and 0.034 to three different portions of the material, and a portion without SiC nanoparticles was retained as a reference. All four samples were subjected to consolidation by hot-pressing. Furthermore, Al2O3 nanoparticles were added in volume fractions of f = 0.01, 0.0216, and 0.0325 to three other portions, again retaining a fourth protion as reference. These four samples were consolidated by spark-plasma sintering. The thermoelectric transport properties of these composites were characterized from 325 to 740 K. For the sample with 0.01 volume fraction of SiC, there was an enhancement in figure of merit by 18 % compared with the reference sample, mainly due to an 18 % reduced thermal conductivity. The 9 % reduction in thermal conductivity of the sample with 0.01 volume fraction of Al2O3 was not enough to compensate the loss in the power factor of 18 %, leading to a decrease in the figure of merit. Microstructural information obtained by SEM, TEM, and BET was used to elucidate the phase and transport properties. The spark-plasma-sintered bulk sample has a figure of merit that is 35 % higher than the bulk sample consolidated through hot-pressing. [ABSTRACT FROM AUTHOR]

Noting the steadily worsening problem of depleted fossil fuel sources, alternate energy sources have become increasingly important; these include thermoelectrics, which may use waste heat to generate electricity. To be economically viable, the thermoelectric figure-of-merit, zT, which is related to the energy conversion efficiency, needs to be in excess of unity ( zT > 1). Tl4SnTe3 and Tl4PbTe3 were reported to attain a thermoelectric figure-of-merit zTmax = 0.74 and 0.71, respectively, at 673 K. Here, the thermoelectric properties of both materials are presented as a function of x in Tl10- xSn xTe6 and Tl10- xPb xTe6, with x varying between 1.9 and 2.05, culminating in zT values in excess of 1.2. These materials are charge balanced when x = 2, according to (Tl+)8(Sn2+)2(Te2−)6 and (Tl+)8(Pb2+)2(Te2−)6 (or: (Tl+)4Pb2+(Te2−)3). Increasing x causes an increase in valence electrons, and thus a decrease in the dominating p-type charge carriers. Larger x values occur with a smaller electrical conductivity and a larger Seebeck coefficient. In each case, the lattice thermal conductivity remains under 0.5 W m−1 K−1, resulting in several samples attaining the desired zTmax > 1. The highest values thus far are exhibited by Tl8.05Sn1.95Te6 with zT = 1.26 and Tl8.10Pb1.90Te6 with zT = 1.46 around 685 K. [ABSTRACT FROM AUTHOR]

Noting the steadily worsening problem of depleted fossil fuel sources, alternate energy sources have become increasingly important; these include thermoelectrics, which may use waste heat to generate electricity. To be economically viable, the thermoelectric figure-of-merit, zT, which is related to the energy conversion efficiency, needs to be in excess of unity ( zT > 1). Tl4SnTe3 and Tl4PbTe3 were reported to attain a thermoelectric figure-of-merit zTmax = 0.74 and 0.71, respectively, at 673 K. Here, the thermoelectric properties of both materials are presented as a function of x in Tl10- xSn xTe6 and Tl10- xPb xTe6, with x varying between 1.9 and 2.05, culminating in zT values in excess of 1.2. These materials are charge balanced when x = 2, according to (Tl+)8(Sn2+)2(Te2−)6 and (Tl+)8(Pb2+)2(Te2−)6 (or: (Tl+)4Pb2+(Te2−)3). Increasing x causes an increase in valence electrons, and thus a decrease in the dominating p-type charge carriers. Larger x values occur with a smaller electrical conductivity and a larger Seebeck coefficient. In each case, the lattice thermal conductivity remains under 0.5 W m−1 K−1, resulting in several samples attaining the desired zTmax > 1. The highest values thus far are exhibited by Tl8.05Sn1.95Te6 with zT = 1.26 and Tl8.10Pb1.90Te6 with zT = 1.46 around 685 K. [ABSTRACT FROM AUTHOR]

Abstract: Various materials of the formulas Mo3−x Fe x Sb7 and Mo2.6Fe0.4Sb7− y Te y have been prepared by solid state synthesis at 873K, starting from the elements in the stoichiometric ratios. The Fe content can be as high as x=0.45, while attempts to incorporate 0.5 Fe lead to the formation of FeSb2 as a minor side product. At x=0.4, the Te content can vary within 0≤y≤0.75, while the sample with y=1.0 shows FeSb2 as a minor phase. The materials were densified via hot-pressing, and their thermoelectric properties determined. Increasing both the Fe and the Te content leads to a decrease in the p-type carrier concentration, and thus an increase in Seebeck coefficient and a decrease in both electrical and thermal conductivity. In the end, the best thermoelectric properties were obtained in case of Mo2.6Fe0.4Sb6.25Te0.75, i.e. at the edge of the phase range, culminating in a figure-of-merit of zT=0.34 at 800K. [Copyright &y& Elsevier]

Tl9BiTe6, a substitution variant of Tl5Te3, is one of the leading midtemperature thermoelectricsand is postulated to exceed ZT= 1 above 450 K whenprepared by zone-melting and reach ZT= 0.86 at 560K after hot-pressing. We have prepared the isostructural series Tl9Sb1–xTe6, Tl9–xSb1+xTe6, Tl9Bi1–xTe6, and Tl9–xBi1+xTe6, with xranging from 0 to 0.05, from the elements in the stoichiometricratios and determined their thermoelectric properties after hot-pressing.In theory, these tellurides are narrow-gap semiconductors when x= 0, with all elements in common oxidation states, accordingto (Tl+)9(Sb/Bi)3+(Te2–)6. The as-prepared samples of this 9-1-6 stoichiometry,however, exhibit relatively high electrical conductivity, which decreaseswith increasing temperature, indicative of the presence of extrinsiccharge carriers. The Seebeck coefficient is generally above +100 μVK–1. Decreasing the Sb and Bi content increasesthe hole carrier concentration and thus increases the electrical conductivitywhile decreasing the Seebeck coefficient. The best feature of thesethermoelectrics is their low thermal conductivity, which is consistentlywell below 0.7 W m–1K–1. In combinationwith reasonable electrical conductivity and a high Seebeck coefficient,high ZTvalues in excess of 1 can also be achievedvia simple hot-pressing after experimental optimization of the carrierconcentration via introducing deficiencies on the Bi site. Moreover,the variants with Sb instead of Bi exhibit similar thermoelectricperformance, a result of the combination of a better electrical performanceand higher thermal conductivity. [ABSTRACT FROM AUTHOR]

n-Type CoSbGeTe ( x = 0.125 to 0.275) compounds with different Te contents have been synthesized by a melt-quench-anneal-spark plasma sintering method, and the effects of Te content on the structure and thermoelectric properties have been investigated. The results show that all specimens exhibited n-type conduction characteristics. The solubility limit of Te in CoSbGeTe is found to be x = 0.25. The solubility of Te in CoSb is increased through charge compensation of the element Ge. The room-temperature carrier concentration N of CoSbGeTe skutterudites increases with increasing Te content, and the compounds possess high power factors. The maximum power factor of 3.89 × 10 W m K was obtained at 720 K for the CoSbGeTe compound. The thermal conductivity decreases dramatically with increasing Te content due to strong point defect scattering. The maximum value of the thermoelectric figure of merit ZT = 1.03 was obtained at 800 K for CoSbGeTe, benefiting from a lower thermal conductivity and a higher power factor. The figure of merit is competitive with values reported for single-filled skutterudites. [ABSTRACT FROM AUTHOR]