Showing papers on "Seebeck coefficient published in 1994"

Some properties of semiconducting IrSb3

Abstract: Polycrystalline p‐type samples of IrSb3 and Ir0.5Rh0.5Sb3 have been made by hot isostatic pressing of powders. A number of properties such as thermal expansion coefficient, sound velocity, thermal conductivity, electrical conductivity, Seebeck coefficient, and carrier concentration have been measured. These compounds show promise as thermoelectric materials.

Thermoelectric figure of merit of superlattices

Abstract: We calculate the electrical conductivity, thermopower, and the electronic contribution to the thermal conductivity of a superlattice, with the electric field and the thermal gradient applied parallel to the interfaces. We include the tunneling between quantum wells. The broadening of the lowest subband when the period of the superlattice is decreased produces a reduction of the thermoelectric figure of merit. However, we found that a moderate increase of the figure of merit may be expected for intermediate values of the period, due to the enhancement of the density of states produced by the superlattice structure.

Transport Anomalies of High-T c Oxides above Room Temperature

Abstract: Transport properties of La 2- x Sr x CuO 4 , YBa 2 Cu 3 O 6+ x and Bi 1.6 Pb 0.5 Sr 1.9- y La y Cu 1.05 O z have been studied over wide temperature regions. Drastic temperature variations of the Hall coefficients R H found in the underdoped region of the hole carriers suggest that there exists a crossover-like change of the electronic state above room temperature. Temperature dependence of other transport properties studied at high temperatures is also discussed in relation to this anomalous behavior of R H . These results elucidate the formation process of the abnormal metallic state of high- T c oxides at low temperatures, the existence of which characterizes the metal-insulator transition of the Cu-oxide system as a new-type Mott-Hubbard transition.

Characterization of transparent conducting CdO films deposited by spray pyrolysis

Abstract: Transparent conducting cadmium oxide (CdO) films have been deposited by spray pyrolysis. The film thicknesses have been determined using Rutherford backscattering spectrometry. X-ray diffraction measurements show that the films are polycrystalline with a preferential orientation along the (111) diffraction plane and the lattice parameter has been calculated. The dislocation density and strain have also been evaluated. The films possess a transmittance of about 75% in the visible and near-infrared region. The refractive index is found to vary between 1.68 and 2.84 in the wavelength range 500-1500 nm. The values of indirect and direct bandgaps obtained are 1.98 and 2.32 eV respectively. Hall effect measurements have been carried out in the temperature range 304-349 K. Resistivity, carrier concentration and mobility of the films at room temperature have been evaluated as 6.6*10-5 Omega m, 1.4*1025 m-3 and 0.68*10-2 m2 V-1 s-1 respectively. Thermoelectric power values from thermoelectric power measurements carried out in the temperature range 304-376 K have been found to be about 19.7-89 mu V K-1. Laser damage studies performed at a wavelength of 1.06 mu m indicate that the films possess a damage threshold density of about 2.37*104 J m-2.

Thermoelectric Effect in Normal-State YBa2Cu3O7-δ Films

Abstract: Signal pulses of several 100 volts and currents of several amperes have been obtained at lateral surface contacts on normal-state YBa2Cu3O7-? films in response to pulsed laser irradiation. The signals are shown to be of thermoelectric origin. Thermoelectric fields transverse to the laser-induced temperature gradient are due to the anisotropy of the thermopower in YBa2Cu3O7-? giving rise to non-zero off-diagonal elements Sij ? of the Seebeck tensor for films prepared with a tilt angle ? between the film c-axis and the film surface normal. Large-tilt-angle films (up to ? = 20?) could be grown on specially cut substrates and may be useful as almost wavelength-independent room temperature radiation detectors.

High-temperature thermoelectric properties of In2O3-based mixed oxides and their applicability to thermoelectric power generation

Abstract: Thethermoelectric properties of mixed oxides In2O3·MOx(MOx= Cr2O3, Mn2O3, NiO, ZnO, Y2O3, Nb2O5 SnO2) are investigated in terms of the thermoelectric materials at high temperature. The Seebeck coefficients,S, of all the samples have negative values, and those of In2O3·SnO2 and In2O3·ZnO increase linearly with temperature, attaining values of –90 and –210 µV K–1 at 1000 °C, respectively. The electrical conductivities, σ, of these oxides are significantly high. The power factor S2σ of the oxides has constantly positive temperature coefficients up to over 1000 °C. Rather low thermal conductivities, κ, of the sintered bodies of the oxides,ca. 1.7 W m–1 K–1 at room temperature, lead to the largest value of the thermoelectric figure of merit Z= 0.4 × 10–4 K–1 for M = Sn at 1000 °C, and the Z value increases toward higher temperatures.

Single‐Electrode Peltier Heats of Li‐Si Alloy Electrodes in LiCl‐KCl Eutectic Melt

Abstract: This paper reports single-electrode Peltier heats for cathodic (or anodic) reactions of Li-Si alloy electrodes in coexisting phase states evaluated from their thermoelectric power values. The thermoelectric power and thermodynamic properties for various coexisting phase states in Li-Si alloy were determined from electromotive force measurements of the following nonisothermal and isothermal cells, respectively, (T) Li I LiCl-KCl I Li-Si (T + ΔT) and (T) Li | LiCl-KCl | Li-Si (T). General methods of estimating the thermoelectric power for a lithium alloy electrode from its thermodynamic properties have been developed thermodynamically. The estimation methods were validated by detailed comparison with experimental results of Li-Si alloy electrode systems.

Crystal Structure and Physical Properties of (BDT-TTP)2ClO4.

Abstract: The ClO4, BF4, and ReO4 salts of BDT-TTP, 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene, are isostructural, having uniform columns of the donor molecules. These salts are essentially metallic down to low temperatures, though the resistivity increases to some extent below 200 K. The thermoelectric power and ESR show simple metal-like behavior down to low temperatures.

Magnetic susceptibility and thermoelectric power of tungsten intermediary oxides

Abstract: The magnetic susceptibility of the tungsten intermediary oxides WO3-x (0.05

Transport properties of single-crystal HgBa2Ca2Cu3O8+δ

Abstract: We report the first measurements of the transport properties of single crystals of HgBa 2 Ca 2 Cu 3 O 8+τ . Data for the in-plane and out-of-plane resistivity, in-plane Hall coefficient and in-plane thermoelectric power of single crystals with onset temperatures as high as 134 K are presented. The in-plane resistivity, Hall coefficient and thermoelectric power all indicate that these crystals are underdoped, which may offer at least a partial explanation for the strong pressure dependence of T c observed in this compound. The in-plane Hall coefficient shows a strong temperature dependence in accord with other cuprate superconductors. A calculation of the cotangent of the Hall angle (cotθ H ) reveals that the relation cot θ H = AT 2 + B is obeyed to high precision in these crystals, despite strong curvature of the in-plane resistivity. Data are also reported for the influence of magnetic field on the resistive transition, for fields of up to 7 T applied both parallel and perpendicular to the crystallographic c -axis. These latter measurements give an estimate for the anisotropy of H c2 , implying a value which is intermediate between that found for YBa 2 Cu 3 O 7−τ and Bi 2 Sr 2 CaCu 2 O 8+ x .

Defect chemistry and transport properties of Pb(Zr1/2Ti1/2)O3

Abstract: In order to gain insight into the degradation mechanisms associated with ferroelectric thin films, such as fatigue and imprint, an understanding of the defect chemistry and transport properties of the material is needed In this study several complimentary techniques have been used to either measure or calculate indirectly the various thermodynamic parameters governing defect formation and transport in Pb(Zr1/2Ti1/2)O3, (PZT) By combining the results of DC equilibrium conductivity, thermoelectric power and the sealed cell techniques, “constant composition oxygen activity” and “constant composition conductivity,” values for the oxidation enthalpy (ΔHox), hole trapping energy (E A) and the enthalpy of motion for holes (ΔE A) have been determined to be −049 eV, ≤09 eV and ≥01 eV, respectively From these results, it is apparent that PZT is an oxygen excess p-type semiconductor in the experimental regime of 500°–700°C and P(O2) ≥ 10−4 atm Furthermore, the results indicate that there is a signifi

Transports in blends of conducting polymers

Abstract: We investigated the transport properties of solution-processed conductive polymer blends of polyaniline-(camhpor sulfonic acid), PANI-CSA, with insulating polymethylmethacrylate (PMMA), as a function of various volume fraction (ƒ) of PANI-CSA. Due to the phase separated morphology and the fibrillar geometry of percolating objects, a self-assembled PANI-CSA network in insulating matrix shows extremely low percolation threshold (ƒc ≈ 0.003). The characteristic metallic properties of pure PANI-CSA, such as positive temperature coefficient of resistivity at high temperature, linear temperature dependence of thermoelectric power, and frequency independent ac conductivity, are retained in PANI-CSA/PMMA blends down to ƒc. At low temperature, the hopping transports through the conducting polymer network depends on the volume fraction of PANI-CSA in blends and its network structure.

The electronic properties of liquid Ag1-xSex

Abstract: Measurements of the electrical conductivity sigma , thermoelectric power S and magnetic susceptibility of liquid Ag1-xSex alloys have been measured as a function of composition and temperature. The unusual maximum in sigma , along with the negative d sigma /dT observed around stoichiometry for Ag-S alloys is also observed in this system. The thermopower shows a p-n transition at x=0.36 with a magnitude indicating that this is a liquid semiconductor with an essentially zero energy gap. It is demonstrated that the results cannot be explained using the Kubo-Greenwood expressions for sigma and S if rigid band behaviour is assumed. The origins of this unusual behaviour are discussed in terms of an enhanced carrier mobility near the stoichiometric composition.

Thermoelectric power generating device

Abstract: A thermoelectric conversion member formed by a thermoelectric conversion element has a split ring shaped transverse cross section. Electrodes are disposed on ring ends of the thermoelectric conversion member facing each other. A magnetic field generating unit generates a magnetic field in a direction perpendicular to the transverse cross-sectional plane of the thermoelectric conversion member. A heating unit for heating one side of an annular wall of the thermoelectric conversion member and a cooling unit provided on the opposite side of the annular wall of the thermoelectric conversion member produces a temperature gradient in a direction radially of the thermoelectric conversion member. Electric field is induced in the direction perpendicular to both directions of the magnetic field and the temperature gradient, that is in the circumferential direction of the ring of the thermoelectric conversion member under the Nernst effect, enabling an electric voltage to be taken out at the electrodes.

Charge Transport of Hydrochloric Acid Doped Polyaniline and Poly(o-toluidine) Fibers: Role of Processing

Abstract: We report the results of transport (temperature dependent dc conductivity, thermoelectric power, and microwave frequency conductivity, and dielectric constant) and structural studies for hydrochloric acid doped polyaniline (PAN-HCl) fibers 4-fold stretched at 300, 350, and 400 "C and the results of dc conductivity for its methyl ring-substituted derivative, poly(o-toluidine) (POT-HCl) fibers. For the PAN- HCl fibers, with increasing stretching temperatures, the system shows greater localization, as indicated by the decreasing conductivity with stronger temperature dependence and decreasing microwave dielectric constant with weaker temperature dependence. This is in accord with the observed decreasing crystallinity with increasing processing temperature. The interrupted metallic strands model is used to account for the microwave results assuming that the size of the metallic regions increases linearly with temperature. For the POT-HC1 fiber, the conductivity is similar to that for the POT-HCl powder. When the fiber is stretched 3-fold, the conductivity increases almost 1 order of magnitude while the temperature dependence changes only slightly, in agreement with the short localization length in the system.

Influence of grain-boundary scattering on the transport-properties of a high-Tc oxide superconductor

Abstract: We report measurements of the resistivity (ϱ( T )), Hall coefficient ( R H ), thermoelectric power ( S ) and AC susceptibility of a polycrystalline sample of Co-doped YBa 2 Cu 3 O 7 in which the grain-boundary resistance could be drastically altered without affecting the properties of the individual grains. Our results show that although the shape and magnitude of ϱ( T ) are strongly changed by the increase in grain-boundary scattering, there is no corresponding effect in either the thermoelectric power or the Hall coefficient. These results suggest that measurements of the temperature dependence of R H and S made on stoichiometric polycrystalline samples should accurately reflect those of the grains.

Skutterudites: A new class of promising thermoelectric materials

Abstract: Based on literature data and experimental findings at the Jet Propulsion Laboratory (JPL), semiconductors with the skutterudite structure TPn3 (where T is a transition metal element such as Co, Rh, Ir, Ni, and Pd, and Pn is a pnicogen element such as P, As, and Sb) possess attractive characteristics and show a good potential for high ZT values. The high degree of covalency results in high mobility and low electrical resistivity values while a relatively complex 32 atom unit cell results in a reasonably low thermal conductivity. Both n‐type and p‐type electrical conductivity samples have been obtained. Room temperature Seebeck coefficient values up to 200 μVK−1 for p‐type and up to −600 μVK−1 for n‐type have also been measured on several of these materials. In addition, the large number of isostructural compounds, solid solutions and related phases offer many possibilities for optimization of the transport properties to a specific temperature range of thermoelectric applications. By replacing the transition metal or the pnicogen atom by two of its neighboring elements and ensuring that the number of valence electrons is retained, many ternary phases can be successfully derived from the original CoAs3 skutterudite structure. Some of these materials were found to have substantially lower thermal conductivities compared to those of the binary compounds. The composition, band gap and doping level can be tailored to achieve maximum performance. An overview of the results obtained to date is provided and our approach to achieving high ZT materials are discussed in this paper.

Point defects and thermoelectric properties of iron disilicide ceramics sintered with SiH4‐plasma‐processed micrograins

Abstract: The point defects in β‐iron disilicide (β‐FeSi2) have been investigated by electron paramagnetic resonance (EPR) along with the thermoelectric properties. The samples used are FeSix (1.9≤x≤2.8) ceramics sintered with FeSix micrograins processed in SiH4‐plasma and nonprocessed. EPR detects (1) several S=1/2 signals and (2) a multiplet signal. An S=1/2 signal with orthorhombic g factors (g1=2.061, g2=2.047, g3=2.024) is detected in all n‐type specimens, and ascribed to unpaired electrons of donors associated with iron vacancies. The other S=1/2 signals are detected in both n‐type and p‐type specimens. The centers responsible for these signals are considered to exist in an oxidized intergrain region of the ceramics. The EPR intensity of the multiplet signal due to the closed‐pair of a high spin Fe3+ ion (S=5/2) and an S=1/2 center is reduced by SiH4‐plasma treatments. SiH4‐plasma processing of FeSix micrograins prior to sintering changes the Seebeck coefficient sign and magnitude, depending upon the conditio...

Electrical Properties of Manganese‐Doped Titanium Dioxide

Abstract: The electrical conductivity and Seebeck coefficient for TiO2 doped with varying amounts of MnO2 have been measured over the temperature range of 900°–1100°C. The Hall coefficient was also measured over the temperature range of 300°–500°C. The electrical conductivity and carrier density were found to decrease initially, go through a minimum at approximately x = 0.0001–0.001, and then increase with increasing content of MnO. For dopant levels above 0.01 at.%, p-type electrical conduction behavior was observed.