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Showing papers on "Seebeck coefficient published in 1998"


Journal ArticleDOI
TL;DR: In this article, the transport properties of polycrystalline Ge clathrates with general composition Sr8Ga16Ge30 are reported in the temperature range 5'K⩽T'⦽300'K.
Abstract: Transport properties of polycrystalline Ge clathrates with general composition Sr8Ga16Ge30 are reported in the temperature range 5 K⩽T⩽300 K. These compounds exhibit N-type semiconducting behavior with relatively high Seebeck coefficients and electrical conductivity, and room temperature carrier concentrations in the range of 1017–1018 cm−3. The thermal conductivity is more than an order of magnitude smaller than that of crystalline germanium and has a glasslike temperature dependence. The resulting thermoelectric figure of merit, ZT, at room temperature for the present samples is 14 that of Bi2Te3 alloys currently used in devices for thermoelectric cooling. Extrapolating our measurements to above room temperature, we estimate that ZT>1 at T>700 K, thus exceeding that of most known materials.

861 citations


Journal ArticleDOI
TL;DR: In this paper, the temperature-dependent thermoelectric power (TEP) of crystalline ropes of single-walled carbon nanotubes was measured and it was shown that the TEP is large and hole-like at high temperatures and approaches zero as T{r_arrow}0.
Abstract: We have measured the temperature-dependent thermoelectric power (TEP) of crystalline ropes of single-walled carbon nanotubes. The TEP is large and holelike at high temperatures and approaches zero as T{r_arrow}0 . The results argue against the opening of a gap at low temperature in these materials. When derived from a simple band structure picture, the TEP of a single metallic nanotube is significantly lower than the measured TEP, strongly suggesting that the predicted electron-hole symmetry of metallic nanotubes is broken when the tubes self-assemble into ropes. Different models for the symmetry breaking are considered. {copyright} {ital 1998} {ital The American Physical Society}

247 citations


Journal ArticleDOI
TL;DR: In this paper, polycrystalline Co3O4 films were prepared by normal pressure chemical vapour deposition, and the d.c. electrical conduction was investigated at temperatures from 170 to 400 K. The Seebeck coefficient indicated the films to be p-type semiconductors.

212 citations


Journal ArticleDOI
TL;DR: In this article, the Seebeck coefficient and electric conductivity in polyaniline and polypyrrole at different doping levels were measured and it was shown that at 300 K, the general correlation that the logarithm of the electrical conductivity varies linearly with the seebeck coefficient on doping, but with a proportionality substantially in excess of a prediction from simple theory for a single type of mobile carrier.
Abstract: We have measured the Seebeck coefficient and electric conductivity in the air-stable conducting polymers polyaniline and polypyrrole at different doping levels. We find, at 300 K, the general correlation that the logarithm of the electrical conductivity varies linearly with the Seebeck coefficient on doping, but with a proportionality substantially in excess of a prediction from simple theory for a single type of mobile carrier. The correlation is unexpected in its universality and unfavorable in its consequences for thermoelectric applications. A standard model suggests that conduction by carriers of both signs may occur in these doped polymers, which thus leads to reduced thermoelectric efficiency. We also show that polyacetylene (which is not air stable), does exhibit the correlation with the expected proportionality, and, thus, its properties could be more favorable for thermoelectricity.

202 citations


Journal ArticleDOI
TL;DR: In this article, the effect of iron doping in thin films deposited by rf sputtering was discussed, and it was shown that iron acts as an acceptor impurity for thin films.
Abstract: The present study discusses the effect of iron doping in thin films deposited by rf sputtering. Iron doping induces a structural transformation from anatase to rutile and electrical measurements indicate that iron acts as an acceptor impurity. Thermoelectric power measurement shows a transition between n-type and p-type electrical conduction for an iron concentration around 0.13 at.%. The highest p-type conductivity at room temperature achieved by iron doping was .

166 citations


Patent
05 May 1998
TL;DR: In this article, the Seebeck coefficient of the sensor lead relative to the first metallic material was shown to be at least ten to one, where the Seebebeck coefficient is defined as the ratio of the temperature at an individual location on an electrode which is formed of a first metal material to the temperature of a second metal material.
Abstract: An apparatus for providing a plurality of signals, each indicative of a temperature at an individual location on an electrode which is formed of a first metallic material includes a plurality of electrically conductive sensor leads, each individually connected to the electrode to form a sensor junction. Each sensor junction has a temperature-dependent voltage associated with it. An electrically conductive common lead is connected to the electrode to form a common junction. The common lead is formed of a second metallic material such that substantially no temperature-dependent voltage is associated with the common junction. Each of the sensor leads is formed of a metallic material different than the first metallic material. Each metallic material has a known Seebeck coefficient relative to the first metallic material. The ratio of the magnitude of the Seebeck coefficient of the sensor lead metallic material relative to the first metallic material and the magnitude of the Seebeck coefficient of the common lead metallic material relative to the first metallic material is at least ten to one. The common lead generally exhibits a thermoelectric output similar to the first metallic material and may be formed of the first metallic material.

128 citations


Journal ArticleDOI
TL;DR: In this article, the dielectric properties of a single crystal of yttrium iron garnet (Y3Fe5O12) were measured in the temperature range 77-725 K and in the frequency range 100 Hz-1 MHz.
Abstract: The dielectric properties (dielectric constant and loss) of a single crystal of yttrium iron garnet (Y3Fe5O12) were measured in the temperature range 77–725 K and in the frequency range 100 Hz-1 MHz. AC conductivity was derived from dielectric constant and loss. DC conductivity was measured in the temperature range 30–725 K. Thermoelectric power (TEP) was measured from 77–800 K. On the basis of the results, conduction in this garnet is interpreted as due to small polarons. The nature of conduction at different temperature ranges is discussed in the light of existing reports on defect formation.

115 citations


Journal ArticleDOI
TL;DR: The Seebeck coefficient was introduced by Peltier and explained by Lord Kelvin this article, who showed that an electrical current passing through the junction of two dissimilar conductors results in the absorption or release of heat in the vicinity of the junction depending on the direction of the current.
Abstract: In materials that conduct both electricity and heat, the thermal and electrical currents are coupled. This thermoelectric coupling can be used to construct devices that act as temperature sensors, heat pumps, refrigerators, or power generators. A temperature difference ΔT across any electrical conductor will generate a corresponding voltage difference ΔV The ratio ΔV/ΔT is defined as the Seebeck coefficient S after Thomas See-beck who first discovered the effect in 1823. Probably the most familiar use of this effect is the thermocouple in which the union of two dissimilar metals generates a voltage in response to an imposed temperature difference. Interestingly an electrical current I passing through the junction of two dissimilar conductors results in the absorption or release of heat in the vicinity of the junction depending on the direction of the current. The ability to heat or cool in this manner was first discovered by Peltier and explained by Lord Kelvin. The latter showed that the amount of heat produced (or absorbed) near the junction is given by ΠI = STI where Π is called the Peltier coefficient and T is the temperature. It is primarily this effect that makes thermoelectric (Peltier) refrigeration possible. Thermoelectric refrigerators and power generators are attractive for many applications as they have no moving parts (except electrons and holes), use no liquid refrigerant, and last indefinitely.

103 citations


Journal ArticleDOI
TL;DR: In this article, the electrical resistivity, thermoelectric power and thermal conductivity have been measured between 4.2 and 300 K on three Bi1−xSbx alloys of different composition (x = 0.144, 0.165 and 0.181).

102 citations


Journal ArticleDOI
TL;DR: In this article, the phase equilibrium and thermoelectric properties of Co1−xFexSb3 ternary system up to high iron context x=0.40 were examined.
Abstract: We have examined the phase equilibrium and thermoelectric properties of Co1−xFexSb3 ternary system up to high iron context x=0.40. Traces of Sb were observed in the hot-pressed samples with x⩾0.06, and FeSb2 (Fe0.73Co0.27Sb2) compound with marcasite structure was also observed in the samples with x⩾0.25 by x-ray diffraction. The lattice parameter of Co1−xFexSb3 is slightly larger than that of the binary compound CoSb3. The Seebeck coefficient and the electrical resistivity are generally reduced by the substitution for Co by Fe. The thermal conductivity is also reduced by the substitution especially at high iron content region. These behaviors of the thermoelectric properties in the samples with low iron content are ascribed to the substituted Fe, while those in the samples with high iron content are ascribed to the precipitated FeSb2 (Fe0.73Co0.27Sb2) compound. For x⩽0.04, the figure of merit for Co1−xFexSb3 decreases with increasing x. However, above x=0.06 the figure of merit increases with x and as a r...

100 citations


Journal ArticleDOI
TL;DR: In this article, the Seebeck coefficient measurements at temperatures from 375-475 K indicated the glasses to be n-type semiconducting, and the d.c. conduction was confirmed to obey the small polaron hopping model, and was due to mainly hopping between V-ions in the glasses.
Abstract: Semiconductive oxide glasses in the system V2O5–MnO–TeO2 were prepared, and the mechanism of d.c. conduction was studied. The Seebeck coefficient measurements at temperatures from 375–475 K indicated the glasses to be n-type semiconducting. The d.c. conductivity ranged from 5×10−5 to 1.9×10−6 S cm−1 at 405 K for V2O5=60 mol% and MnO=0–20 mol%, and decreased with increasing MnO content. The conduction was confirmed to obey the adiabatic small polaron hopping model, and was due to mainly hopping between V-ions in the glasses. The polaron band width J was estimated to be J=0.10–0.20 eV. The electron–phonon interaction coefficient γp was very large (21–26). The hopping mobility evaluated as 2.3×10−7–2.7×10−6 cm2 V−1 s−1 increased with increasing V2O5 content. The estimated carrier concentration was the order of 1019 cm−3. The principal factor determining conductivity was the polaron hopping mobility in these glasses. © 1998 Chapman & Hall

Journal ArticleDOI
TL;DR: In this paper, thin films of AgInO2 were prepared to find a transparent and n-type conducting oxide with a delafossite structure, which is a candidate material for fabricating a pn junction with the recently found p type conducting and transparent CuAlO2 delafosite.
Abstract: Thin films of AgInO2 were prepared to find a transparent and n-type conducting oxide with a delafossite structure. This is a candidate material for fabricating a pn junction with the recently found p type conducting and transparent CuAlO2 delafossite. Nondoped and 5% Sn-doped thin films were deposited on a silica glass substrate by radio-frequency sputtering. The crystalline phase in the films was identified to be the delafossite structure by x-ray diffraction and chemical composition was confirmed to be an Ag/In ratio=1.00/0.97 by inductively coupled plasma emission spectroscopy. The optical band gap was estimated from absorption spectra to be ∼4.4 eV, and the thin films were transparent up to near ultraviolet region. Electrical conductivities of the nondoped and 5% Sn-doped AgInO2 films at room temperature were 1×10−5 and 6×100 S cm−1, respectively. Measurements of Hall voltage and Seebeck coefficient (−50 μV K−1) suggested the conduction in the Sn-doped film to be n type. Carrier concentration and Hall mobility in the doped film were 2.7×1019 cm−3 and 0.47 cm2 V−1 s−1, respectively.

Journal ArticleDOI
TL;DR: In this article, the authors applied measurements of the thermoelectric power of 5 mol % Sr-substituted LaPO 4 as a function of temperature (600 to 900°C), water vapor partial pressure (0.2 to 6 kPa), and oxygen partial pressure(4 to 100 kPa).
Abstract: Measurements of the thermoelectric power were applied to investigate the electrical conductivity in 5 mol % Sr-substituted LaPO 4 as a function of temperature (600 to 900°C), water vapor partial pressure (0.2 to 6 kPa), and oxygen partial pressure (4 to 100 kPa). Expressions of the thermoelectric power for materials conducting protons, oxide ions, and electronic defects were derived, based on a thermodynamic treatment of entropy production by heat and charge transfer. The experimental data for 5 mol % Sr-substituted LaPO 4 were interpreted in terms of protonic conduction, and some additional conduction, possibly by electron holes. In air, the proton transport number is unity at 600°C when p H2 O > 1 kPa, and at 700°C when p H2 O > 3 kPa. In wet atmospheres, the transported entropy of protons in this material was found to be nearly constant, 112 ± 2 J mol -1 K -1 at 600 to 800°C in wet atmospheres.

Journal ArticleDOI
TL;DR: In this article, the phonon thermal conductivity of Zn0.98Al0.02O was suppressed by adding MgO to ZnO to suppress the thermal conductivities of the material.
Abstract: Addition of MgO to Al-doped ZnO was successful in reduction of the phonon thermal conductivity,κph , in order to suppress the unfavorably high thermal conductivity, κ, of the material in terms of applications to thermoelectric conversion. The electrical conductivity, σ, of Zn0.98Al0.02O decreased with increasing amount of the added MgO, whereas the Seebeck coefficient was virtually unchanged up to (Zn0.9Mg0.1)0.98Al0.02O. Further Al2O3 doping was ineffective in improving σ. The carrier mobility decreased with increasing amount of the added MgO but was independent of the extent of the Al doping. In spite of the significant suppression of κ, the figure of merit was smaller for the MgO-added samples because of the marked decrease of σ.

Journal ArticleDOI
TL;DR: In this paper, a hexagonal Cu-2 Te has been synthesized by mechanical alloying from elemental powders, and the milling time required for the synthesis is longer than that reported for other tellurides.

Journal ArticleDOI
TL;DR: In this article, tetragonal thin films of phase were obtained by thermal evaporation technique; the as-deposited films were non-crystalline and the crystallinity was built in on annealing at 423 K. The films showed n-type conduction; the existence of two distinct activation energies and belongs to two types of level.
Abstract: Stoichiometric thin films of were prepared by the thermal evaporation technique; the as-deposited films were non-crystalline and the crystallinity was built in on annealing at 423 K. The crystal structure as determined by both x-ray and electron diffraction showed that tetragonal films of phase were obtained. Both dark electrical resistivity and thermoelectric power (Seebeck coefficient S) were measured for films before and after annealing. The films showed n-type conduction; the existence of two distinct activation energies and belongs to two types of level: a shallow level of before annealing and after annealing and deep levels of for as deposited films and for annealed film. The deep level was also detected by the space charge limited current technique and the trap density is found to be . The obtained results are explained on the basis of an energy diagram of - proposed by Garlick.

Journal ArticleDOI
TL;DR: In this paper, the thermoelectric figure of merit for a compound material comprising thin semiconductor and wider metallic layers is calculated for a material with a very high ZT if the distance between the barriers is on the order of the energy relaxation length.
Abstract: The thermoelectric figure of merit is calculated for a compound material comprising thin semiconductor and wider metallic layers. The layers are perpendicular to the direction of current. The semiconductor barriers exclude electrons with energies e<μ from the current. This exclusion increases thermopower. One may obtain a material with a very high ZT if the distance between the barriers is on the order of the energy relaxation length. This material should have the resistivity characteristic of a metal and the thermopower characteristic of a semiconductor. An additional significant rise in ZT can be achieved by increasing the contact area at the metal–semiconductor interface.

Journal ArticleDOI
TL;DR: In this paper, the authors reported local density approximation of the electronic structure and thermoelectric properties of a low carrier density metal with a complex Fermi-surface topology and a nontrivial dependence of the Hall concentration on the band filling.
Abstract: We report local-density-approximation calculations of the electronic structure and thermoelectric properties of $\ensuremath{\beta}\ensuremath{-}{\mathrm{Zn}}_{4}{\mathrm{Sb}}_{3}$. The material is a low carrier density metal with a complex Fermi-surface topology and a nontrivial dependence of the Hall concentration on the band filling. The band structure is rather covalent, consistent with experimental observations of good carrier mobility. At a band filling corresponding to the experimental Hall number, the calculated thermopower and temperature dependence are in good agreement with experiment. The high Seebeck coefficient in a metallic material is remarkable, and arises in part from the strong energy dependence of the Fermi surface topology near the experimental band filling. An improved thermoelectric performance is predicted for lower doping levels, i.e., higher Zn concentrations.

Journal ArticleDOI
TL;DR: The thermoelectric, electric and structural properties of Bi 2 Te 3 thin films grown by MOCVD have been investigated as mentioned in this paper The Seebeck coefficient shows that all the samples were n-type conductors decreasing from 213 to 129μV/K when the carrier concentration increases from 9×10 19 to 3×10 20 cm −3.

Journal ArticleDOI
TL;DR: In this paper, a cylindrical Bridgman ampoule with a uniform axial magnetic field, a planar crystal-melt interface, a parabolic temperature variation along the interface and two different uniform values of the absolute thermoelectric power for the melt and crystal was treated.

Journal ArticleDOI
TL;DR: In this article, the authors performed simultaneous measurements of electrical conductivity and thermoelectric power of holes and oxide ions under oxygen partial pressure, PO 2, between 10−14 and 1 atm using dried O2+Ar and CO+CO2 gas mixtures.

Journal ArticleDOI
TL;DR: In this paper, the growth of Bi 2 Te 3 thin films by metal organic chemical vapour deposition (MOCVD) using diethytellurium and trimethylbismuth as tellurium or bismuth sources respectively is investigated on pyrex substrates.

Journal ArticleDOI
TL;DR: In this article, the degenerate temperature, scattering parameter, bandgap energy, and the effective masses of the electron and hole have been determined for SbI3 and CuBr-doped Bi2Te3-15% Bi2Se3 single crystals at temperatures ranging from 77 to 600 K.

Journal ArticleDOI
TL;DR: In this article, a comparative analysis of the Hall effect, conductivity, and thermopower properties of molecular-beam-epitaxy-grown GaN is presented, showing that hopping in the acceptor band contributes significantly to the electronic transport properties.
Abstract: A comparative investigation of the Hall effect, conductivity, and thermopower properties of molecular-beam-epitaxy-grown GaN is presented. In unintentionally doped n-type GaN, a negligible thermal activation of the thermopower is observed above 300 K. In as-grown GaN:Mg, a thermopower activation energy of 280 meV is observed at high temperatures, as well as a scattering factor $A=3.$ At temperatures below 120 K, the Seebeck coefficient of p-type GaN changes sign and indicates n-type conductivity. These results show that hopping in the acceptor band contributes significantly to the electronic transport properties. After hydrogenation of GaN:Mg, both conductivity and thermopower have an activation energy of 520 meV, which is at variance with the presence of potential fluctuations in the material. This demonstrates that hydrogen passivates Mg-doped GaN by the formation of electrically inactive Mg-H complexes, in contrast to the formation of compensating H-related donors, which should lead to noticeable potential fluctuations.

Journal ArticleDOI
TL;DR: In this article, electrical resistivity, thermoelectric power, and high-pressure x-ray-diffraction measurements are carried out to investigate the anomaly observed earlier in fusion data around 3 GPa in the intermetallic compound.
Abstract: Electrical resistivity, thermoelectric power, and high-pressure x-ray-diffraction measurements are carried out to investigate the anomaly observed earlier in fusion data around 3 GPa in the intermetallic compound ${\mathrm{AuIn}}_{2}.$ While the imaging plate high-pressure angle-dispersive data indicate a structural phase transition beyond 8 GPa, the thermoelectric power shows a peak around 2 GPa, indicating the occurrence of an electronically driven isostructural transition. The first-principles linearized muffin-tin orbital calculations reveal that this transition is brought about by interception of the Fermi level by the energy-band maximum. The Lifshitz nature of this transition is responsible for the anomaly in the high-pressure electrical and fusion data.

Journal ArticleDOI
TL;DR: In this paper, the authors showed that β-Cu2−xSe (0.20≤x≤0.25) showed a transition to a two-phase mixture of (α+β) at ∼250 K, and then the β phase transformed to an ordered new phase at 180 K, characterized by the jump of electrical resistivity ρ, Hall coefficient RH, Seebeck coefficient S and magnetic susceptibility χ.

Journal ArticleDOI
TL;DR: In this paper, total electrical conductivity and thermoelectric power measurements of polycrystalline Y 2 Ti 2 O 7 were made at 1373, 1273, 1173 and 1073 K under the oxygen partial pressure, p O 2, between 10 −23 and 1.0 atm using Ar+O 2, H 2 +H 2 O, H 2+CO 2, and CO +CO 2 and gas mixtures.

Journal ArticleDOI
TL;DR: In this paper, the temperature dependence of the Hall mobility, Seebeck coefficient, electrical resistivity, thermal conductivity, and figure-of-merit of the SbI3 and CuBr-doped 85% Bi2Te3-15% bi2Se3 single crystals have been characterized at temperatures ranging from 77 K to 600 K.
Abstract: The temperature dependence of the Hall mobility, Seebeck coefficient, electrical resistivity, thermal conductivity, and figure-of-merit of the SbI3 and CuBr-doped 85% Bi2Te3-15% Bi2Se3 single crystals have been characterized at temperatures ranging from 77 K to 600 K. The scattering parameter in 85% Bi2Te3-15% Bi2Se3 single crystal was determined as 0.1 from the temperature dependence of the carrier mobility. With increasing the amount of Sbl3 or CuBr doping, the Seebeck coefficient of 85% Bi2Te3-15% Bi2Se3 decreased and the temperature at which the Seebeck coefficient shows a maximum shifted to higher temperature. Compared to the Sbl3-doped specimens, the CuBr-doped single crystals exhibited higher (m* / m0)3/2 μc, implying that CuBr is a more effective dopant to improve the material factor and thus the figure-of-merit of 85% Bi2Te3-15% Bi2Se3. The maximum figure-of-merit of 2.0 × 10−3/K and 2.2 × 10−3/K was obtained for 0.1 wt % Sbl3-doped specimen and 0.03 wt % CuBr-doped specimen, respectively.

Journal ArticleDOI
TL;DR: In this paper, the effect of small amounts of Ti substitutional doping (M1−xTixTe5, where M=Hf, Zr) on the thermoelectric properties is reported.
Abstract: The thermoelectric properties (resistivity and thermopower) of single crystals of the low dimensional pentatelluride materials, HfTe5 and ZrTe5, have been measured as a function of temperature from 10 K

Journal ArticleDOI
TL;DR: In this article, the CoFe2O4 ferrite thin films have been prepared by spray pyrolysis technique at different substrate temperatures (Ts) and the XRD patterns reveal a good (111) texture in the film prepared at Ts=325°C.