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Showing papers on "Seebeck coefficient published in 2003"


Journal ArticleDOI
TL;DR: In this paper, the authors provide a critical summary of some recent developments of new concepts and new materials in thermoelectric materials research, including quantum wells, superlattices, quantum wires, and quantum dots.
Abstract: Efficient solid state energy conversion based on the Peltier effect for cooling and the Seebeck effect for power generation calls for materials with high electrical conductivity σ, high Seebeck coefficient S, and low thermal conductivity k. Identifying materials with a high thermoelectric figure of merit Z(= S2σ/k) has proven to be an extremely challenging task. After 30 years of slow progress, thermoelectric materials research experienced a resurgence, inspired by the developments of new concepts and theories to engineer electron and phonon transport in both nanostructures and bulk materials. This review provides a critical summary of some recent developments of new concepts and new materials. In nanostructures, quantum and classical size effects provide opportunities to tailor the electron and phonon transport through structural engineering. Quantum wells, superlattices, quantum wires, and quantum dots have been employed to change the band structure, energy levels, and density of states of elect...

932 citations


Journal ArticleDOI
22 May 2003-Nature
TL;DR: The finding—that spin-entropy dominates the enhancement of thermopower in transition-metal oxides—for the search for better Peltier materials is discussed.
Abstract: In an electric field, the flow of electrons in a solid produces an entropy current in addition to the familiar charge current. This is the Peltier effect, and it underlies all thermoelectric refrigerators. The increased interest in thermoelectric cooling applications has led to a search for more efficient Peltier materials and to renewed theoretical investigation into how electron-electron interaction may enhance the thermopower of materials such as the transition-metal oxides. An important factor in this enhancement is the electronic spin entropy, which is predicted to dominate the entropy current. However, the crucial evidence for the spin-entropy term, namely its complete suppression in a longitudinal magnetic field, has not been reported until now. Here we report evidence for such suppression in the layered oxide Na(x)Co2O4, from thermopower and magnetization measurements in both longitudinal and transverse magnetic fields. The strong dependence of thermopower on magnetic field provides a rare, unambiguous example of how strong electron-electron interaction effects can qualitatively alter electronic behaviour in a solid. We discuss the implications of our finding--that spin-entropy dominates the enhancement of thermopower in transition-metal oxides--for the search for better Peltier materials.

544 citations


Journal ArticleDOI
TL;DR: In this paper, single crystals of (Ca2CoO3)0.7CoO2 were grown using a modified strontium chloride flux technique, and their electrical and thermal properties were determined.
Abstract: Single crystals of (Ca2CoO3)0.7CoO2 were grown using a modified strontium chloride flux technique, and their electrical and thermal properties were determined. Growth conditions were established for obtaining plate-like single crystals of a relatively large size (5×10×0.05 mm3). At 973 K, thermoelectric power S and electrical resistivity ρ of the specimens are ≈240 μV K−1 and ≈2.3×10−5 Ω m, respectively, and their thermal conductivity κ is nearly 3 W m1 K−1, as determined by mathematical extrapolation. The figure of merit ZT=S2T/ρκ derived therefrom is ≈0.87 at 973 K. The relatively low κ is likely the result of a misfit structure between the CoO2 layer and the Ca2CoO3 slab.

445 citations


Journal ArticleDOI
TL;DR: Thermoelectric power (TEP) of individual single walled carbon nanotubes (SWNTs) has been measured at mesoscopic scales using a microfabricated heater and thermometers and strong modulations of TEP were observed in the single-electron conduction limit.
Abstract: Thermoelectric power (TEP) of individual single walled carbon nanotubes (SWNTs) has been measured at mesoscopic scales using a microfabricated heater and thermometers. Gate electric field dependent TEP modulation has been observed. The measured TEP of SWNTs is well correlated to the electrical conductance across the SWNT according to the Mott formula. Strong modulations of TEP were observed in the single-electron conduction limit. In addition, semiconducting SWNTs exhibit large values of TEP due to the Schottky barriers at SWNT-metal junctions.

271 citations


Journal ArticleDOI
TL;DR: In this article, the thermoelectric properties of Sr0.9R0.1TiO3 (R=Y, La, Sm, Gd, Dy) have been measured from room temperature to 1073 K.

256 citations


Journal ArticleDOI
TL;DR: In this article, the authors presented first principles transport calculations for electrons and holes at levels up to 10−21−4 GPa and showed that the electrical conductivity, the Seebeck coefficient, and the power factor are derived from the calculated transport distribution.
Abstract: We present first-principles transport calculations for ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ using the linearized-augmented plane-wave method and the relaxation time approximation. We considered the effects of hydrostatic pressure and uniaxial stress up to 4 GPa. Doping was included for electrons and holes at levels up to ${10}^{21}/{\mathrm{cm}}^{3}.$ The electrical conductivity, the Seebeck coefficient, and the power factor are derived from the calculated transport distribution. Our results for the electronic structure and the transport properties are in qualitative agreement with experiment. Furthermore, we predict a large increase in the power factor under applied uniaxial stress.

163 citations


Journal ArticleDOI
TL;DR: In this paper, the thermal conductivity, electrical conductivity and Seebeck coefficient of hot-pressed Al 2 O 3 added ZnO ceramic samples were measured in dependence of temperature up to 600°C.
Abstract: Al 2 O 3 added ZnO powders were prepared via sol–gel processing, using zinc acetate, ammonia and Al 2 O 3 powders as starting materials. Scanning electron microscopy (SEM) observations indicated that the Al 2 O 3 added ZnO powders consisted of very fine particles (0.1–2 μm). The thermal conductivity, electrical conductivity and Seebeck coefficient of hot-pressed Al 2 O 3 added ZnO ceramic samples were measured in dependence of temperature up to 600 °C. The influence of Al 2 O 3 addition on the thermoelectric (TE) properties of ZnO ceramics is discussed.

152 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed a mechanism for enhancement of the thermoelectric figure-of-merit in regimented quantum dot superlattices, which can be tuned in such a way that electrical current is mostly through the well-separated minibands of relatively large width.
Abstract: We propose a mechanism for enhancement of the thermoelectric figure-of-merit in regimented quantum dot superlattices. A proof-of-concept calculation has been carried out for p-type regimented superlattice of Ge dots on Si. It is shown that when conditions for miniband formations are satisfied, carrier transport in such structures can be tuned in a favorable way leading to large carrier mobility, Seebeck coefficient, and, as a result, to the thermoelectric figure-of-merit enhancement. To maximize the improvement, one has to tune the parameters of quantum dot superlattice in such a way that electrical current is mostly through the well-separated minibands of relatively large width (at least several kBT, where kB is Boltzmann’s constant and T is temperature).

151 citations


Journal ArticleDOI
TL;DR: In this article, a plate-like Ca3Co4O9 was prepared in which Bi and Na were partially substituted for Ca to improve the thermoelectric performance, and a highly oriented TGG + HP specimen showed high electrical conductivity compared with the specimen sintered under uniaxial pressure (UP + PLS).
Abstract: Plate-like particles of Ca3Co4O9 have been prepared in which Bi and Na were partially substituted for Ca to improve the thermoelectric performance. Successfully fabricated dense and highly textured ceramics have been obtained by combining the templated grain growth technique (TGG) with hot-pressing (HP). Ca3Co4O9 single crystals, which have alternating layers of Co–O and Ca–Co–O in the direction of the c-axis, show high electrical conductivity along the layer compared with that across the layer. Hence, a highly oriented TGG + HP specimen showed high electrical conductivity compared with the specimen sintered under uniaxial pressure (UP + PLS). The improved electrical conductivity with high Seebeck coefficient of the highly oriented specimen (TGG + HP) gave a high thermoelectric power factor of 5.9 × 10−4 W m−1 K−2 at 1073 K. The figures-of-merit at 773 K and 1073 K were calculated to be 8.54 × 10−5 K−1 (ZT = 0.066 at 773 K) and 1.69 × 10−4 K−1 (ZT = 0.18 at 1073 K), respectively. These values are quite high among Ca–Co–O polycrystalline systems reported so far.

144 citations


Journal ArticleDOI
TL;DR: In this article, the partial Nd filling on skutterudite compounds is discussed in the context of potential thermoelectric materials, and the effect of the partial filling on the transport properties is discussed.
Abstract: Polycrystalline samples of the partially filled skutterudites NdxCo4Sb12 have been prepared and characterized by x-ray powder diffraction and differential thermal analysis. The saturation limit of the Nd void filling in CoSb3 was found to be around 13%. All samples decompose incongruently at a temperature of 1149 ± 6 K. Room temperature Hall measurements show that each Nd atom donates approximately 0.8 electrons, which is significantly less than the Nd oxidation state (3+). The temperature dependence of the electrical and thermal transport properties has been measured over the range of 11–700 K. The electrical resistivity and absolute value of the Seebeck coefficient decrease with increasing Nd content and for samples with x > 0.02 the temperature dependence is typical of heavily doped semiconductors. Filling CoSb3 with Nd causes a rapid initial decrease in the lattice thermal conductivity with a minimum at the composition Nd0.1Co4Sb12. Nd-filled skutterudites exhibit the lowest value of the lattice thermal conductivity in comparison with other partially filled skutterudites at x < 0.1, which could be attributed to a smaller radius of Nd than that of other filling elements. At high temperature the ZT value of the Nd-filled skutterudites is limited due to intrinsic conduction caused by the relatively low carrier concentration. The effect of the partial Nd filling on the transport properties of the filled skutterudite compounds is discussed in the context of potential thermoelectric materials.

140 citations


Journal ArticleDOI
TL;DR: In this paper, the mesoscopic experimental measurements of electron energy dissipation, phonon thermal transport, and thermoelectric phenomena in individual carbon nanotubes have been discussed.

Journal ArticleDOI
TL;DR: P-type transparent conducting thin films of copper aluminium oxide were prepared by DC sputtering of polycrystalline CuAlO 2 target, which was fabricated by heating a stoichiometric mixture of Cu 2 O and Al 2 O 3 at 1375 K for 24 hours as discussed by the authors.

Journal ArticleDOI
TL;DR: In this paper, structural and electron transport properties of Se-and Te-doped CoSb 3 skutterudites in relation to results of electronic structure calculations performed for this system were presented.

Journal ArticleDOI
TL;DR: In this paper, several hot-pressed samples based on β-Zn 4 Sb 3 with different amounts of ZnSb or Zn were prepared and their thermoelectric properties were investigated in a temperature range from room temperature (R.T.) to 673 K.

Journal ArticleDOI
TL;DR: In this paper, thin films of p-type Bi05Sb15Te3, n-type bi2Te27Se03, and n- type (Bi2Te3)90(Sb2Te-3)5(sb2Se3) 5 (with 1 3 1/3 % SbI3) were deposited on substrates of mica and aluminum nitride (on silicon) using pulsed laser ablation at substrate temperatures between 300°C to 500°C.
Abstract: Thin films of p-type Bi05Sb15Te3, n-type Bi2Te27Se03, and n-type (Bi2Te3)90(Sb2Te3)5(Sb2Se3)5 (with 013 wt % SbI3) were deposited on substrates of mica and aluminum nitride (on silicon) using pulsed laser ablation at substrate temperatures between 300 °C to 500 °C The films were characterized using x-ray diffraction and transmission electron microscopy for crystalline quality and epitaxial growth on the substrates The surface morphology and microstructure were examined using scanning electron microscopy X-ray mapping and energy-dispersive spectroscopy were performed to determine nonstoichiometry in the composition and homogeneity The quality of the films, in terms of stoichiometric composition and crystal perfection, was studied as a function of growth temperature and laser fluence The values of the Seebeck coefficient, electrical resistivity, and Hall mobility in the thin films were measured and compared with those in the bulk Thermoelectric figure of merit of the films was evaluated from the

Journal ArticleDOI
TL;DR: In this paper, high grain-aligned Ca3Co4O9 and (Ca2.7Sr0.2La0.1)O9 ceramics were treated by a spark plasma sintering process to increase their bulk densities.
Abstract: Highly grain-aligned Ca3Co4O9 and (Ca2.7Sr0.2La0.1)(Co3.9Cu0.1)O9 ceramics were prepared by the magnetic alignment technique, and then treated by a spark plasma sintering process to increase their bulk densities. Thermoelectric properties were investigated from room temperature to 700 °C in air. Grain alignment is effective in lowering the electrical resistivity and has no obvious influence on the Seebeck coefficient, thus resulting in enhancement of the thermoelectric power factor. Substitution of Sr, La and Cu does not appreciably change the electrical resistivity and Seebeck coefficient, but significantly reduces the thermal conductivity.

Journal ArticleDOI
TL;DR: In this paper, physical properties of the thermoelectric oxide NaCo 2 O 4 are briefly reviewed and attributed to the substantially enhanced effective mass, which comes from the large entropy of Co 4+ in the low spin state.
Abstract: Physical properties of the thermoelectric oxide NaCo 2 O 4 are briefly reviewed. The high thermoelectric properties of this material are attributed to the substantially enhanced effective mass, which comes from the large entropy of Co 4+ in the low spin state. The large entropy confined in the CoO 2 block causes a spin-density-wave transition at 22 K upon Cu substitution for Co, which can be regarded as “order from disorder”.

Journal ArticleDOI
TL;DR: In this paper, the phase equilibrium and thermoelectric properties of Co1−xNixSb3 ternary system were examined up to high nickel content x=0.40 by x-ray diffraction.
Abstract: The phase equilibrium and thermoelectric properties of Co1−xNixSb3 ternary system were examined up to high nickel content x=0.40. NiSb compound with nickel arsenide structure was observed as the impurity phase in the samples with x>0.10 by x-ray diffraction. The sign of the Seebeck coefficient of Co1−xNixSb3 is negative, and the absolute value of the Seebeck coefficient and electrical resistivity generally decreases with increasing x. The thermal conductivity is reduced in the samples with x⩽0.06, but above x=0.06 it increases with increasing x. These behaviors of the thermoelectric properties in the samples with low nickel content are ascribed to the substituted Ni, while those in the samples with high nickel content are ascribed to the precipitated NiSb compound. In order to more reduce the thermal conductivity of the material, we have prepared a sintered CoSb3–NiSb composite where the NiSb particles are dispersed in the CoSb3 matrix by mechanical grinding and hot pressing. The thermal conductivity of t...

Journal ArticleDOI
TL;DR: In this paper, the authors measured the thermoelectric power of carbon nanotube materials doped with acids and attributed this unusual behavior to 1D phonon drag, in which the depression of the Fermi energy cuts off electron-phonon scattering at temperatures below a characteristic T 0.
Abstract: We measured thermoelectric power S of bulk single-wall carbon nanotube materials p doped with acids. In contrast to oxygen-exposed or degassed samples, S is very small at the lowest temperatures, increases superlinearly above a characteristic and sample-dependent T, and then levels off. We attribute this unusual behavior to 1D phonon drag, in which the depression of the Fermi energy cuts off electron-phonon scattering at temperatures below a characteristic T0. This idea is supported by a model calculation in which the low temperature behavior of phonon drag is specifically related to the one-dimensional character of the electronic spectrum.

Journal ArticleDOI
TL;DR: In this paper, a focus is placed on half-Heusler-type compounds with additions of Hf, Zr, Si, or Pt. Alloy additions strongly affect not only thermoelectric properties but also phase stability.
Abstract: Half-Heusler-type compounds have gained increasing attention as promising thermoelectric materials. In the present work, a focus is placed on TiNiSn with additions of Hf, Zr, Si, or Pt. Nominally stoichiometric TiNiSn alloys were prepared using arc melting and subsequent annealing at 1,073 K for 2 weeks. The thermoelectric properties, such as thermoelectric power, electrical resistivity, and thermal conductivity, were measured in a temperature range from 300 K to 1,000 K. As-cast materials show metallic transport properties, while annealed ones exhibit semiconductor behavior. Microstructures of TiNiSn alloys basically consist of nonequilibrium four-phase; half-Heusler TiNiSn, Heusler TiNi2Sn, metallic Ti6Sn5, and Sn solid solution. The volume fraction of the half-Heusler TiNiSn phase significantly increases by annealing. It is revealed that coexisting metallic phases degrade the thermoelectric properties of half-Heusler TiNiSn. Alloy additions strongly affect not only thermoelectric properties but also phase stability. The thermal conductivity of TiNiSn alloys with alloy additions decreases because of the point-defect phonon scattering.

Journal ArticleDOI
TL;DR: The high-temperature thermoelectric properties of single-crystal Ca3Co2O6, which consists of parallel one-dimensional Co2O66− chains separated by Ca2+ ions, are measured to be a potential candidate for use as a thermoeLECTric material at high temperatures by virtue of being chemically stable up to 1300 K.
Abstract: We measured the high-temperature thermoelectric properties of single-crystal Ca3Co2O6, which consists of parallel one-dimensional Co2O66− chains separated by Ca2+ ions. The resistivity (ρ) along the c-axis decreases rapidly upon increasing temperature from 2×104 to 8 mΩ cm in a temperature region of 300 to 1073 K. The Seebeck coefficient (S) is positive and is 230 and 160 μV/K at 373 and 1073 K, respectively. The thermal conductivity (κ) is as low as 8 W/mK at room temperature and decreases linearly with the increase of temperature to 4.6 W/mK at 773 K. Thus, the estimated dimensionless figure-of-merit [ZT=(S2/ρκ)T (T: absolute temperature)], is about 0.15 at 1073 K. As the thermoelectric figure-of-merit (Z), shows a sharp rise in the measured temperature range, Ca3Co2O6 is expected to possess high thermoelectric efficiency at higher temperatures, and is considered to be a potential candidate for use as a thermoelectric material at high temperatures by virtue of being chemically stable up to 1300 K.

Journal ArticleDOI
TL;DR: In this article, the temperature dependent thermoelectric power (TEP) of boron- and nitrogen-doped multiwalled carbon nanotube mats has been measured showing that such dopants can be used to modify the majority conduction from p-type to n-type.
Abstract: The temperature dependent thermoelectric power (TEP) of boron- and nitrogen-doped multiwalled carbon nanotube mats has been measured showing that such dopants can be used to modify the majority conduction from p-type to n-type. The TEP of boron-doped nanotubes is positive, indicating hole-like carriers. In contrast, the nitrogen doped material exhibits negative TEP over the same temperature range, suggesting electron-like conduction. Therefore, the TEP distinct nonlinearities are primarily due to the formation of donor and acceptor states in the B- and N-doped materials. The sharply varying density of states used in our model can be directly correlated to the scanning tunneling spectroscopy studies of these materials.

Journal ArticleDOI
TL;DR: In this paper, a polycrystalline-sintered sample of Tl9BiTe6 has been prepared by hot pressing, and the thermoelectric properties have been measured in the temperature range from room temperature to about 700 K.

Journal ArticleDOI
TL;DR: In this article, BaCuQF (Q=S,Se) materials, candidate transparent p-type conductors, were prepared by solid-state reaction, and their bulk electrical and optical properties were evaluated.
Abstract: BaCuQF (Q=S,Se) materials, candidate transparent p-type conductors, were prepared by solid-state reaction, and their bulk electrical and optical properties were evaluated. The room-temperature Seebeck coefficient and electrical conductivity of undoped BaCuQF pellets were +56 μV/K and 0.088 S/cm, respectively, for the sulfide fluoride, and +32 μV/K and 0.061 S/cm, respectively, for the selenide fluoride. The conductivity was greatly enhanced by the substitution of several percent of K for Ba; the highest conductivities were 82 S/cm for Ba0.9K0.1CuSF and 43 S/cm for Ba0.9K0.1SeF. The band gaps for Q=S and Q=Se were measured to be 3.2 and 3.0 eV, respectively. Undoped BaCuSF exhibits strong red luminescence near 630 nm under ultraviolet excitation.

Journal ArticleDOI
TL;DR: In this article, the output power of 15 different types of flat thermoelectric panels exposed to two thermal fluids was derived from heat transfer theory, and written by non-dimensional functions to reflect the characteristics of system design.

Journal ArticleDOI
TL;DR: In this paper, the effects of Cu and Ge additions on β-FeSi2 alloys were investigated, and the effect of the amount of both dopants on their thermoelectric properties was investigated.

Journal ArticleDOI
TL;DR: In this article, the oxygen permeability, total conductivity and Seebeck coefficient of La2Ni0.9Co0.1O4+δ were studied in the oxygen partial pressure range of 10−16 Pa to 50 kPa at 973-1223 K.
Abstract: The oxygen permeability, total conductivity and Seebeck coefficient of La2Ni0.9Co0.1O4+δ were studied in the oxygen partial pressure range of 10−16 Pa to 50 kPa at 973–1223 K. The conductivity of La2Ni0.9Co0.1O4+δ is predominantly p-type electronic within the whole p(O2) range in which the K2NiF4-type structure exists. Thermally-activated mobility, the values of which are 0.02–0.08 cm2 V−1 s−1, and the p(O2) dependencies of electron-hole transport suggest a small-polaron conduction mechanism. Oxygen permeability of dense La2Ni0.9Co0.1O4+δ membranes, with an apparent activation energy of 192 kJ mol−1 in oxidising conditions, is limited by both bulk ionic conductivity and the surface exchange rate. The role of surface processes in limiting permeation is also significant under air/H2–H2O gradients and increases with decreasing temperature. The stability boundary of the La2Ni0.9Co0.1O4+δ phase at low oxygen pressures is similar to that of undoped lanthanum nickelate, which allows stable operation of nickelate membranes under high oxygen chemical potential gradients, such as air/10% H2–90% N2, at 973 K. At temperatures above 1000 K, the decomposition products form blocking layers on the membrane surface causing degradation of the membrane performance with time. The average thermal expansion coefficient of La2Ni0.9Co0.1O4+δ ceramics, calculated from dilatometric data in air, is 12.8 × 10−6 K−1 at 400–1265 K.

Journal ArticleDOI
TL;DR: In this paper, the authors attribute this oscillatory behavior to quantum-size effects, which are observable when the electron mean-free path and Fermi wave length exceed the film thickness d.
Abstract: Oscillatory thickness dependences of the electrical conductivity, Hall coefficient, charge carrier mobility, and Seebeck coefficient were obtained at room temperature for n-type thin Bi films (d=3–300 nm) fabricated by the thermal evaporation of a bismuth crystal in a vacuum and deposition on mica substrates at 380 K. We attribute this oscillatory behavior to quantum-size effects, which are observable when the electron mean-free path and Fermi wave length exceed the film thickness d.

Journal ArticleDOI
TL;DR: In this paper, the microstructure and thermoelectric properties of the compounds were investigated as a function of extrusion temperature and the fabricated powder consists of homogeneous Bi 2 Te 3 +Bi 2 Se 3 solid solution and the relative density of over 99% was obtained by hot extrusion.

Journal ArticleDOI
TL;DR: In this article, single-crystal-like polycrystals of misfit-layered cobaltites were fabricated using an in situ topotactic conversion of aligned reactive seed particles.
Abstract: For high-temperature thermoelectric power generators, single-crystal-like polycrystals of misfit-layered cobaltites were fabricated using an in situ topotactic conversion of aligned “reactive seed” platelet particles and the highly textured ceramics exhibited strong anisotropy with improved electrical conductivity.