Thermal Transport Properties of TlInTe2 Single Crystals (original) (raw)
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Anisotropic thermal conductivity and thermopower of In 2 Te 5 single crystal
Thermopower and thermal conductivity of the electron-doped manganite La 0.9 Te 0.1 Mn O 3 Abstract. We present here the anisotropic transport properties (thermal conductivity and Seebeck coefficient) in a single crystal of In 2 Te 5 with the thermal gradient applied parallel and perpendicular to the crystallographic c-axis of the crystal. The thermal conductivity along the c-direction (κ || ) is found to be less (0.41W/m-K) than the thermal conductivity perpendicular to the c-direction ( κ ⊥ = 0.91 W/ m-K) at 300 K. At the same time, the thermopower parallel to the cdirection (S || ) is found to be higher than its value for the perpendicular direction (S ⊥ ). These improvements can be taken as an indication that the In 2 Te 5 compound is a good candidate belonging to the family of thermoelectric materials.
Extrapolation of Transport Properties and Figure of Merit of a Thermoelectric Material
Energies, 2015
The accurate determination of the thermoelectric properties of a material becomes increasingly difficult as the temperature rises. However, it is the properties at elevated temperatures that are important if thermoelectric generator efficiency is to be improved. It is shown that the dimensionless figure of merit, ZT, might be expected to rise with temperature for a given material provided that minority carrier conduction can be avoided. It is, of course, also necessary that the material should remain stable over the whole operating range. We show that the prediction of high temperature properties in the extrinsic region is possible if the temperature dependence of carrier mobility and lattice thermal conductivity are known. Also, we show how the undesirable effects arising from mixed or intrinsic conduction can be calculated from the energy gap and the relative mobilities of the electrons and the positive holes. The processes involved are discussed in general terms and are illustrated for different systems. These comprise the bismuth telluride alloys, silicon-germanium alloys, magnesium-silicon-tin and higher manganese silicide.
Solid State Phenomena, 2011
We present a study of the electronic properties of Tl5Te3, BiTl9Te6 and SbTl9Te6 compounds by means of density functional theory based calculations. The optimized lattice constants of the compounds are in good agreement with the experimental data. The band gap of BiTl9Te6 and SbTl9Te6 compounds are found to be equal to 0.589 eV and 0.538 eV, respectively and are in agreement with the available experimental data. To compare the thermoelectric properties of the different compounds we calculate their thermopower using Mott’s law and show, as expected experimentally, that the substituted tellurides have much better thermoelectric properties compared to the pure compound.
Growth and Electrical Characterization of TlInTe2 Single Crystal
Journal of King Abdulaziz University-Science, 2008
High efficiency design for single crystal growth from melt based on Bridgman technique is constructed locally and used for growing TlInTe 2 crystals. Measurements of Hall coefficient and DC electrical conductivity covering a temperature range from 158 to 473 K were conducted. The investigated samples have P-Type conductivity with R H of 2.3 × 10 9 cm 3 /coul. at room temperature and carrier concentrations as 2.81×10 9 cm-3. Energy gap ∆E g and ionization energy ∆E a were estimated as 0.72 eV and 0.113 eV, respectively. The diffusion coefficient, diffusion length, as well as relaxation time were evaluated, and the scattering mechanism of charge carrier was checked.
Journal of Electronic Materials, 2013
For bulk thermoelectrics, improvement of the figure of merit ZT to above 2 from the current values of 1.0 to 1.5 would enhance their competitiveness with alternative technologies. In recent years, the most significant improvements in ZT have mainly been due to successful reduction of thermal conductivity. However, thermal conductivity is difficult to measure directly at high temperatures. Combined measurements of thermal diffusivity, specific heat, and mass density are a widely used alternative to direct measurement of thermal conductivity. In this work, thermal conductivity is shown to be the factor in the calculation of ZT with the greatest measurement uncertainty. The International Energy Agency (IEA) group, under the implementing agreement for Advanced Materials for Transportation (AMT), has conducted two international round-robins since 2009. This paper, part II of our report on the international round-robin testing of transport properties of bulk bismuth telluride, focuses on thermal diffusivity, specific heat, and thermal conductivity measurements.
2013
For bulk thermoelectrics, improvement of the figure of merit ZT to above 2 from the current values of 1.0 to 1.5 would enhance their competitiveness with alternative technologies. In recent years, the most significant improvements in ZT have mainly been due to successful reduction of thermal conductivity. However, thermal conductivity is difficult to measure directly at high temperatures. Combined measurements of thermal diffusivity, specific heat, and mass density are a widely used alternative to direct measurement of thermal conductivity. In this work, thermal conductivity is shown to be the factor in the calculation of ZT with the greatest measurement uncertainty. The International Energy Agency (IEA) group, under the implementing agreement for Advanced Materials for Transportation (AMT), has conducted two international round-robins since 2009. This paper, part II of our report on the international round-robin testing of transport properties of bulk bismuth telluride, focuses on thermal diffusivity, specific heat, and thermal conductivity measurements.
Thermoelectric Properties of TlGdQ2 (Q = Se, Te) and Tl9GdTe6
Journal of Electronic Materials, 2012
The ternary thallium chalcogenides TlGdQ 2 (Q = Se, Te), and Tl 9 GdTe 6 were synthesized, and their thermoelectric properties were evaluated. The chalcogenides TlGdQ 2 are isostructural with TlSbQ 2 (space group R " 3m), adopting the a-NaFeO 2 structure type, and Tl 9 GdTe 6 is isostructural with Tl 9 BiTe 6 (space group I4/mcm). TlGdSe 2 was found to be a wide-bandgap semiconductor with rather high Seebeck coefficient and low electrical conductivity. The corresponding telluride TlGdTe 2 behaves like a doped semiconductor, and possesses very low thermal conductivity at room temperature on the order of 0.5 W m À1 K À1 , a property advantageous for thermoelectric applications. Tl 9 GdTe 6 exhibits relatively high room-temperature electrical conductivity of around 850 X À1 cm À1 and a low Seebeck coefficient of 27 lV K À1 , yielding a low power factor. Of these three compounds, TlGdTe 2 exhibits the best thermoelectric properties, with maximum dimensionless figure of merit in the measured temperature regime of 0.5 at 550 K.
First-principles study on thermoelectric transport properties of Ca3Si4
Physical Review Materials
Thermoelectric properties of a semiconducting silicide, Ca 3 Si 4 , were investigated by first-principles calculations. The calculation results revealed that Ca 3 Si 4 has a relatively low lattice thermal conductivity of around 1.2 Wm −1 K −1 at 800 K. The Seebeck coefficients and the electrical conductivities of Ca 3 Si 4 were evaluated by using the Boltzmann transport equation with an energy-dependent relaxation time under the assumption of electron scattering by acoustic phonons. The Seebeck coefficient of n-type Ca 3 Si 4 along the x axis is larger than that along the z axis, while the Seebeck coefficient of p-type Ca 3 Si 4 along the x axis is smaller than that along the z axis. The electrical conductivity of p-type Ca 3 Si 4 is higher than that of n-type Ca 3 Si 4 owing to the smaller effective mass of holes, which results in the higher power factor of p-type Ca 3 Si 4. Maximum ZT (a dimensionless figure of merit) of single-crystalline p-type Ca 3 Si 4 is higher than that of n-type Ca 3 Si 4 , reaching 0.9 at 800 K. Grain-size effects on the lattice thermal conductivities and power factors were also investigated. Reducing lattice thermal conductivities overcomes the decrease of electrical conductivities and thereby enhances ZT , taking maximum of 1.0 for n-type Ca 3 Si 4 and 1.5 for p-type Ca 3 Si 4 when the grain size is 10 nm.
Thermoelectric properties of TlSbTe2 doped with In and Yb
Journal of Alloys and Compounds, 2019
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
Electrical and thermal transport property studies of high-temperature thermoelectric materials
1984
The first year of this research emphasized the study of electronically conducting oxides with varied transport characteristics, an evaluation of theoretical models, and the determination of a high-temperature transport property data base. Oxide systems based on SnO2-In2O3, (La, Y) (Mg,Ca,Sr) CrO3, HfO2-RxOy-In3O3 and La(Sr)MnO3 were selected for initial studies and represent different crystallographic/defect structures and transport characteristics. The electrical conductivity, Seeback coefficient and thermal conductivity for these oxides are being measured and have provided a preliminary data base for evaluating transport properties and the figure of merit. The purpose of this report is to describe the technical results obtained during the first year's study of high-temperature thermoelectric materials. The scope of the research is (1) to develop theoretical models for electrical, thermal, and thermoelectric behavior of refractory oxide materials, (2) to determine electrical t...