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In this study, thermoelectric properties of MgTi 2 O 5 -based composites were investigated. 10–30 vol.% TiN were added as a conductive reinforcement phase. MgTi 2 O 5 /TiN composites were successfully synthesized at 1373 K for 10 min via reactive spark plasma sintering. The present SPS process itself enhanced electrical conductivity of MgTi 2 O 5 more than 250 times while effectively suppressing thermal conduction by defect engineering. Moreover, compositing further remarkably improved its electrical conductivity, and hence large enhancements in the thermoelectric power factor and ZT value were achieved. The results indicate a new doping technique in MgTi 2 O 5 and enhancing thermoelectric properties of other insulating oxide materials. Image, graphical abstract [ABSTRACT FROM AUTHOR]

p -type TlSbTe 2 and its In- and Yb-doped variants were prepared by hot pressing of the elements in the stoichiometric ratios, and their thermoelectric properties were determined after verifying the purity of the samples by powder X-ray diffraction. Theoretically, TlSbTe 2 is an intrinsic semiconductor possessing a narrow band gap; however, the as-prepared TlSbTe 2 exhibited relatively high electrical conductivity, decreasing with ascending temperature, which provides evidence for the presence of p -type extrinsic charge carriers (holes) along with the positive Seebeck coefficient. Doping In onto the Tl site inserts more electrons, thereby decreasing the hole concentration; as a result, the electrical and thermal conductivity decreased and the Seebeck coefficient increased. The best thermoelectric performance of In-doped TlSbTe 2 was achieved at 625 K, with a figure of merit (zT) of 0.77. The overall best zT was improved to 0.85 at 620 K with the sample of nominal composition Tl 0.98 SbYb 0.02 Te 2. An anisotropy test was implemented by comparing the electrical conductivity and Seebeck coefficient measured on the prismatic bars cut parallel and vertical to the pressing direction. The results indicate basically isotropic behavior in polycrystalline TlSbTe 2 along these two orthogonal directions. • TlSbTe2 is bestowed with an extraordinarily low thermal conductivity. • Our processing conditions caused an increase in the figure-of-merit by 15%. • Doping with Yb caused a further increase by an additional 20%, for a total increase of 39%. • Doping with In led to no significant changes in performance. • Direction-dependent measurements revealed no significant anisotropies in the electrical properties. [ABSTRACT FROM AUTHOR]

A series of samples with the initial formula Mo 3– x Fe x Sb 7 and Mo 3– x Ni x Sb 7 have been prepared by solid state reaction at 873 K, starting from the elements in the stoichiometric ratios. The materials were compressed via hot-pressing, and their thermoelectric properties determined. Single crystal data show that Ni atoms in part occupy the cubic voids of the Mo 3 Sb 7 structure, as well as replace some Mo atoms, in contrast to the Fe analogues, where we found no evidence for Fe in the cubic voids. Supported by electronic structure calculations, replacing Mo with Fe or Ni increases the valence-electron count, thus decreases the numbers of p -type carriers of Mo 3 Sb 7 . On the other hand, filling the holes with Ni atoms appears to have no such effect. As a consequence, the Ni containing samples exhibit higher electrical conductivity than the Fe analogues, and ultimately lower thermoelectric figure-of-merit, as the p -type carrier concentration remains too high. [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]

We present the thermoelectric properties of the quaternary telluride series Tl10- x- ySn xBi yTe6 including Seebeck coefficient ( S), electrical conductivity ( σ), and thermal conductivity ( κ). Three different Tl concentrations, namely 9, 8.67, and 8.33 Tl per formula unit, were selected followed by variations of the Sn:Bi ratio to tune the properties at each Tl concentration. Additionally, crystal structure data and electronic structure calculations were used to model the data and support the findings. The Tl9(Sn, Bi)Te6 system was found to have the highest power factor ( S2 σ) displaying a value of 8.1 μW ·cm-1 ·K-2 at 587 K, realized with Tl9Sn0.2Bi0.8Te6. Tl8.67Sn0.50Bi0.83Te6 however, displays values closer to 4 μW ·cm-1 ·K-2 at comparable temperatures. Ultimately, the thermoelectric Figure-of-merit was determined to reach a competitive 0.6 at 575 K and 525 K for Tl8.33Sn1.12Bi0.55Te6 and Tl8.67Sn0.50Bi0.83Te6, respectively, thereby outperforming the ternary variants Tl10- xSn xTe6. [ABSTRACT FROM AUTHOR]

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]

Nearly single phase samples of Tl9LnTe6 (Ln: La, Ce, Pr, Nd, Sm, Gd, Tb) and Tl10-xLaxTe6 (x = 0.9-1.1) are prepared by melting of the elements (C-coated evacuated quartz tubes, 1200 K, 24 h). [ABSTRACT FROM AUTHOR]