Showing papers on "Seebeck coefficient published in 1993"
TL;DR: Calculations show that this approach has the potential to achieve a significant increase in the figure of merit over both the bulk value and the calculated two-dimensional superlattice values.
Abstract: We investigate the effect on the thermoelectric figure of merit of preparing materials in the form of one-dimensional conductors or quantum wires. Our calculations show that this approach has the potential to achieve a significant increase in the figure of merit over both the bulk value and the calculated superlattice values.
2,416 citations
TL;DR: In this article, the effects of substrate temperature on the composition and microstructure of BiSb•Te•Se thin films are discussed and related to the Seebeck coefficient and resistivity.
Abstract: The effects of the substrate temperature on the composition and microstructure of Bi‐Sb‐Te‐Se thin films are discussed and related to the Seebeck coefficient and resistivity. The films were prepared on silica substrates by argon ion beam sputtering. The effect of subsequent heat treatment is also discussed. The composition becomes stoichiometric at the substrate temperature around 500 K at which the Seebeck coefficient has a maximum and the resistivity has a minimum. The Seebeck coefficient changes its sign at the substrate temperature around 340 K. The crystal structure of the films deposited at room temperature is identified as the rock‐salt type, and the change of the thermoelectric properties as a function of the substrate temperature can be mainly attributed to the volume fraction of the Bi2Te3 and rock‐salt structures. The subsequent heat treatment is effective in improving the power factor of the stoichiometric thin films.
136 citations
TL;DR: The temperature dependence of the thermoelectric power was investigated for the emeraldine salt form of polyaniline protonated with camphor sulfonic acid and for blends of PANI-CSA with poly(methyl methacrylate) (PANI-C SA/PMMA).
Abstract: The temperature dependence of the thermoelectric power was investigated for the emeraldine salt form of polyaniline protonated with camphor sulfonic acid (PANI-CSA) and for blends of PANI-CSA with poly(methyl methacrylate) (PANI-CSA/PMMA). The thermoelectric power (S) of PANI-CSA increases linearly in proportion to the temperature with S\ensuremath{\approxeq}+10 \ensuremath{\mu}V/K at room temperature. This characteristic behavior persists when the fraction of PANI-CSA is diluted as a blend in insulating PMMA, even at volume fractions of PANI-CSA as low as about 1%. We discuss the PANI-CSA results in the context of transport at the metal-insulator boundary. The data from the blends are consistent with charge transport along the self-organized interconnected pathways of PANI-CSA in PMMA.
70 citations
TL;DR: In this article, the structure and physical properties of Ni foils were investigated using transmission electron microscopy and X-ray diffraction, and the results showed that the properties deviated from those of equilibrium, coarse-grained physical properties could be attributed to the nanocrystalline structure of the deposits.
62 citations
TL;DR: The microscopic origin of the giant magnetoresistance in metallic superlattices is ascribed to spin-dependent random exchange potential caused by roughness of the interfaces.
Abstract: The microscopic origin of the giant magnetoresistance in metallic superlattices is ascribed to spin-dependent random exchange potential caused by roughness of the interfaces. The random exchange potential is determined self-consistently by calculating the electronic structure and magnetic moments near the interfaces for Fe/TM and Co/TM superlattices, where TM's denote the transition-metal elements. The tight-binding d-band model and recursion method are used in the calculation. The lifetime of electrons is estimated from the imaginary part of the self-energy produced by scattering of electrons by the random exchange potential. The material dependence of the magnetoresistance in Fe/TM and Co/TM superlattices is systematically studied and compared with the experimental results. An expression of the thermoelectric power is derived and its relation to the magnetoresistance is clarified. The material dependence of the thermoelectric power is also discussed.
62 citations
TL;DR: In this article, a polycrystalline, 10μm size magnesium silicide was prepared by alloying 99.9% purity poly crystalstalline silicon obtained from rice husk ash and high-purity magnesium powder.
Abstract: Polycrystalline, 10μm size magnesium silicide was prepared by alloying 99.9% purity polycrystalline silicon obtained from rice husk ash and high-purity magnesium powder. The material in sintered pellet form was characterized for its structural, electrical, thermal, thermoelectric and other properties. A typical sintered pellet exhibited a room-temperature (30°C) thermoelectric power of 565 μV K−1 and an electrical resistivity of 35 Ω cm. On the other hand, the material was found to be thermally quite stable up to 650°C with a room-temperature thermal conductivity of 6.3×10−3cals−1cm−1K−1 (2.6 J s−1 m−1 K−1). These properties of the material indicate that the material can find potential applications as a thermoelectric generator and in other semiconductor devices. Furthermore, an indigenous technology for large-scale production of silanes (SiH4) can be developed using this Mg2Si which could be prepared in large quantities by a simple and low-cost process.
61 citations
TL;DR: In this article, the Ga 1− x Fe x CuMnO 4 system has been studied for the decomposition of 1-octanol, and the activation energy for electronic conduction varied between 0.35 and 0.135 eV. All the catalysts exhibited cubic symmetry and p-type semiconductivity.
52 citations
TL;DR: In this paper, a systematic investigation of the orthorhombic borides LiAlB 14, MgAlb 14, and ErAlB14 was carried out, where several indirect allowed optical interband transitions with phonon emission were derived from transmission measurements in the absorption edge range.
51 citations
TL;DR: In this article, the electrical conductivity and thermoelectric power of polyaniline/PVC blends were measured, and it was shown that the conductivity of the blends is greater at low temperatures than that of the pure polyaniniline sample.
Abstract: The electrical conductivity and thermoelectric power of polyaniline/PVC blends was measured. Surprisingly, the conductivity of the blends is greater at low temperatures than that of the pure polyaniline sample. The conductivity follows approximately an exp(-T -1/2 ) law over a considerable range of temperature, with deviations from this law observed at high temperatures. The thermoelectric power has metallic magnitude, and increases as temperature increases (with positive sign) except at very low temperatures, where negative peaks are observed. Possible models to interpret these observations are mentioned
47 citations
TL;DR: In this paper, the results of the field-effect conductance, conductivity, thermoelectric power, thermoabsorption and electroabsorption measurements are presented, and the results may be explained by assuming a distribution of gap states.
45 citations
TL;DR: In this paper, be-doped cubic boron nitride powders were sintered at 7.7 GPa and 2100°C without the addition of any sintering aids.
Abstract: Be‐doped cubic boron nitride (c‐BN) powders, prepared at 5 GPa and 1700 °C by using Li3BN2 as a catalyst, were sintered at 7.7 GPa and 2100 °C without the addition of any sintering aids. The polycrystals so obtained were p‐type semiconductors as determined by the electric and thermoelectric methods. Nonlinear current‐voltage characteristics, showing similar behavior to that of varistors, were observed by a four‐probe method. The activation energy of the resistivity in the ohmic region at temperatures from 25 to 700 °C was about 0.3 eV.
TL;DR: In this paper, a polyacetylene iodine-doped to saturation level changed from metallic to nonmetallic states by aging, judging from the temperature dependence of the resistivity.
TL;DR: In this paper, the Seebeck coefficient was used to determine the mechanism of electrical transport and defect structure of Cadoped Mn perovskites in the +3 and +4 valence states and a new defect model was developed which includes the thermally excited disproportion of Mn 3+ and Mn 4+ pairs.
TL;DR: In this paper, the thermopower (Seebeck coefficient, S ) has been measured on a series of Co/Cu multilayers that exhibit giant negative magnetoresistance (GMR).
TL;DR: In this article, the electrical transport properties (Hall coefficient, d.c. conductivity, Hall mobility and thermoelectric power) of bismuth selenide thin films prepared by reactive evaporation method were studied in the temperature range from liquid nitrogen to 420 K.
TL;DR: In this article, the effect of air exposure to high temperature thin film thermocouples was evaluated and solutions to the problem were found, where the Seebeck coefficient of a platinum 10% rhodium element was reduced 50% compared to the as-sputtered condition.
Abstract: Thin film thermocouples have the advantage of extremely fast response (≤1 ms), low cost, and very fine spatial resolution. These capabilities have permitted measurements never before possible, such as the instantaneous temperature measurements of the inside surfaces of a diesel engine cylinder during operation. Although these type S platinum plus platinum 10% rhodium thermocouples are stable at the 900–1100 °C range, oxidation of rhodium can take place in the 600–800 °C range in air which lessens the thermoelectric potential of the positive element. We evaluated the effect of air exposures to high temperature thin film thermocouples and attempted to find solutions to the problem. We found that after 50 h at 750 °C the Seebeck coefficient of a platinum 10% rhodium element was reduced 50% compared to the as‐sputtered condition. The reduction of Seebeck coefficient at 700 and 800 °C was also substantial. This reduction in Seebeck coefficient could be recovered by annealing the thin film at 900 °C. The degrad...
TL;DR: In this article, the electronic specific heat coefficient γ could be determined from the specific heat data measured at low temperature, considering that weak electron localization does not significantly affect the γ values.
Abstract: La 2- x Sr x CaCu 2 O 6 samples were prepared at 1050°C under 20 atm oxygen pressure. By various kinds of measurements, it was found that their superconducting volume fractions were very small due to the presence of weak electron localization caused by oxygen deficiency. Then, the electronic specific heat coefficient γ could be determined from the specific heat data measured at low temperature, considering that weak localization does not significantly affect the γ values. The results show that as the hole carrier density of the high- T c Cu oxide system decreases or the system approaches the metal-insulator boundary from the metallic side, γ decreases in contrast to the cases of other Mott-Hubbard systems.
TL;DR: The Wiedemann-Franz law is found to be satisfied over the whole temperature range investigated, which is mainly ascribed to dominant large-angle elastic scattering processes.
Abstract: Thermal conductivity and thermoelectric power have been measured between 2 K and 300 K on granular Co20Ag80 solids. As in ordinary metals, thermal conductivity is largely dominated by the electronic contribution. The Wiedemann-Franz law is found to be satisfied over the whole temperature range investigated, which is mainly ascribed to dominant large-angle elastic scattering processes. Giant magnetothermal conductivity has been observed in accordance with the giant magnetoresistance effect. The magnetothermoelectric power is negative and increases with temperature.
TL;DR: The Seebeck coefficient data did not support the assumption that Mn is present in Ca-doped Mn perovskites only in the +3 and +4 valence states, and a new defect model was developed which includes the thermally excited disproportionation of Mn,[sup 3+] into Mn[sup 2+] and Mn[Sup 4+] pairs.
Abstract: Electrical conductivity and the Seebeck coefficient of compositions in the system Y[sub 1-y]Ca[sub y]MnO[sub 3] and La[sub 1-y]Ca[sub y]MnO[sub 3] were studied to determine the mechanism of electrical transport and defect structure. Electrical conduction appeared to occur via a small polaron hopping mechanism for compositions with 0.30 [le] y [le] 0.80. The Seebeck coefficient data did not support the assumption that Mn is present in Ca-doped Mn perovskites only in the +3 and +4 valence states. A new defect model was developed which includes the thermally excited disproportionation of Mn[sup 3+] into Mn[sup 2+] and Mn[sup 4+] pairs. The Seebeck data were explained with this model by assuming that divalent Mn cations were site blockers in the conduction process.
TL;DR: The thermoelectric power (TEP) of Tl 2 Ba 2 Ca 1-x Y x Cu 2 O 8+y samples as a function of temperature in the temperature range 77-300 K is reported.
Abstract: We report the thermoelectric power (TEP) of Tl 2 Ba 2 Ca 1-x Y x Cu 2 O 8+y (x=0-0.6) samples as a function of temperature in the temperature range 77-300 K. For the x=0 sample (T c =85 K), the room-temperature value of the TEP is negative. For x>0, the TEP is positive and its magnitude increases with increasing x (decreasing carrier concentration). A comparative study of our results with that of other high-T c systems shows that the room-temperature value of the TEP is almost zero for samples with T c ∼T c max
TL;DR: In this article, a large glass formation region was found i.e., ZnO = 0-60mol, V2O5=0-70mol, TeO2=30-100mol, and glasses were found to be n-type semiconductors.
Abstract: Glasses in the system of V2O5-ZnO-TeO2 glasses were prepared by rapid quenching and their dc-condutivity was studied. A large glass formation region was found i.e., ZnO=0-60mol%, V2O5=0-70mol%, TeO2=30-100mol%. The glasses were found to be n-type semiconductors. Dc-conductivities (σ) were in the range from 9.5×10-7 to 5.7×10-7S⋅cm-1 at 473K for V2O5=30-60mol%. The conduction was due to adiabatic small polaron hopping and non-adiabatic small polaron hopping for the glasses with V2O5>50 and V2O5<50mol%, respectively. The polaron band width (J) was estimated to be 0.01-0.10eV. The evaluated carrier mobilities μ were in the range from 4.1×10-8 to 8.9×10-7cm2⋅V-1⋅s-1 at 473K. The values of J and μ satisfied the conditions for the small polaron hopping conduction. The estimated carrier density (NC) was 0.15×1021-2.89×1021cm-3, depending upon V2O5 concentration. Seebeck coefficients (Q) of the glasses determined in the temperature range of 100-200°C exhibited no temperature dependence, and thus it is concluded that the dominant factor responsible for Q was the amount of V4+.
TL;DR: In this article, the electrical resistivity and Seebeck coefficient of ferromagnetic semiconductors GaV4S8 and GAV4Se8 between 20 K and 350 K have been measured.
Abstract: The electrical resistivity and Seebeck coefficient of ferromagnetic semiconductors GaV4S8 and GaV4Se8 between 20 K and 350 K have been measured. These compounds have a cation-deficient spinel composition with Gallium-vacancy ordering and clustering of vanadium atoms into metallic bonded tetrahedra. For the stoichiometric phase, the Arrhenius plots of resistivity show a strong downward curvature; the activation energy Eap of GaV4S8 varies from 0.14 eV at room temperature to 0.04 eV at 80 K. The authors also report AC conductivity measurements between 400 Hz and 200 kHz on stoichiometric GaV4S8. They find that the sigma AC( omega , T) behaviour is similar to that of a Fermi glass and sigma AC( omega ) approximately omega s; s=0.3-0.8 between 50 and 20 K. The substitution of sulphur by selenium or imperfect ordering of Ga vacancies results in a constant Ea of about 0.13 eV over a wide temperature interval. The thermopower behaviour is very sensitive to the quality of the sample and indicates charge transport in a narrow band. These properties are discussed in relation to the special structural features of cluster compounds.
TL;DR: In this paper, the effect of grain size on the thermoelectric figure of merit of heavily doped p-type silicon germanium alloys is compared to earlier results on similar materials.
Abstract: The recent results of C. B. Vining, W. Laskow, J. O. Hanson, R. R. Van der Beck, and P. D. Gorsuch [J. Appl. Phys. 69, 4333 (1991)] regarding the effect of grain size on the thermoelectric figure of merit of heavily doped p‐type silicon germanium alloys are compared to earlier results on similar materials. The data confirm that the room‐temperature figure‐of‐merit is significantly increased in materials with a small grain size.
TL;DR: In this paper, the electrical conductivity and thermopower of thin films were investigated as a function of their microstructure for different ratios [Si]/[Cr] > 1 and concentrations co and cN up to 50 at.%.
TL;DR: In this article, single crystals of Mo0.005Se2 have been grown by direct vapour transport technique to the maximum size 21 mm×15 mm and the growth conditions, growth mechanism and lattice parameters are determined.
TL;DR: In this article, a new mechanism is introduced to account for the maximum ρ c vs T curve observed in some low stage compounds, a new model is proposed and a comment on the semiconductor-like T-dependence of ρ C in high stage GICs is presented.
Abstract: Theory of the c -axis conduction in graphite intercalation compounds was proposed by Sugihara and by Shimamura. Though two theories apparently seem to be different, the underlying physics is the same. In this article the previous treatments are largely revised and extended. To account for a maximum of ρ c vs T curve observed in some low stage compounds, a new mechanism is introduced and a comment on the semiconductor-like T-dependence of ρ c in high stage GICs, is presented. An expression of the c -axis thermoelectric power is derived in connection with ρ c in the low stage compounds.
TL;DR: In this paper, the temperature dependence of the ordinary 4-terminal conductivity, VSC conductivity and thermoelectric power of polythiopene (PT) and poly(3-methylthiophene) (PMeT) was studied.
TL;DR: Seebeck coefficients were measured for the fuel cell (T[sub 1],p)Pt/O[sub 2]),g)/YSZ/O [sub 2]-g)/Pt(T[ sub 2],p),p as discussed by the authors.
Abstract: Seebeck coefficients were measured for the fuel cell (T[sub 1],p)Pt/O[sub 2](g)/YSZ/O[sub 2](g)/Pt(T[sub 2],p). The electrolyte was yttria-stabilized zirconia (YSZ) and the content of yttria in the electrolyte varied between 3 and 12 mole percent (m/o). Thus tetragonal and cubic crystal structures were investigated. Different sintering temperatures and times were used in sample preparation to produce different grain sizes in the electrolyte. The reference temperature is T[sub 1] = 1,000 C and T[sub 2] has been varied up to 1,200 C. Two different oxygen pressures were used. The transported entropy of oxygen ions calculated from the Seebeck coefficient at 1,273 K, is constant and equal to 42 [plus minus] 2 J/KF for all samples. The heat of transport q* is irrelevant to the Seebeck coefficient, as q* is related to diffusion, which does not take place. The Thomson coefficient of the material is estimated to be 18 J/KF. This result is used to compare values for the transported entropy of oxygen ions calculated from literature reports. Common expressions from thermoelectric theory are rejected on theoretical as well as experimental grounds.
TL;DR: In this paper, a phenomenological description of the anomalous behavior of S is proposed, based on the electron damping which has an asymmetric form with respect to the chemical potential µ.
Abstract: Thermoelectric powers S of La 2- x Sr x Cu 1- y M y O 4 (M=Zn and Ni) and YBa 2 Cu 3- y Zn y O 7-δ are measured for various values of x and y . A phenomenological description of the anomalous behavior of S is proposed, based on the electron damping which has an asymmetric form with respect to the chemical potential µ. The Zn doping seems to suppress the anomalous contribution of the electrons to various physical quantities, while the Ni-doping does not.
TL;DR: In this paper, the authors studied the thermoelectric power of the electrons under magnetic quantization in III-V, II-VI, PbTe/PbSnTe and strained layer superlattices with graded interfaces and compared the same with the corresponding bulk specimens of the constituent materials.
Abstract: We study the thermoelectric power of the electrons under magnetic quantization in III–V, II–VI, PbTe/PbSnTe and strained layer superlattices with graded interfaces and compare the same with the corresponding bulk specimens of the constituent materials by formulating the respective expressions incorporating the broadening. It is found, by taking GaAs/Ga1−x Al x As, CdS/CdTe, PbTe/PbSnTe and InAs/GaSb superlattices with graded interfaces as examples, that the thermoelectric power exhibits oscillatory dependence with the inverse quantizing magnetic field due to Shubnikov-de Hass effect and increases with decreasing electron concentration in an oscillatory manner in all the aforementioned cases. The thermopower in graded superlattices is greater than that of constituent bulk materials together with the fact that the oscillations in superlattices show up much more significantly as compared to the respective constituent materials. In addition, the well-known expressions for bulk specimens of wide-gap semiconductors have also been obtained as special cases from our generalized expressions under certain limiting conditions.