Showing papers on "Seebeck coefficient published in 1988"
TL;DR: In this paper, the electrical conductivity and thermopower of cubic Mn3O4 were measured in the temperature range 920° to 1530°C, and the concentrations of Mn4+ and Mn3+ were governed by the disproportionation equilibrium 2Mnoct3+⇄MNOct4++ Mnoct2+.
Abstract: The electrical conductivity and thermopower of Mn3O4 were measured in the temperature range 920° to 1530°C. Electrical conduction in cubic Mn3O4 is explained by the small polaron hopping of electron holes between Mn4+ and Mn3+ on octahedral sites. The concentrations of Mn4+ and Mn3+ are governed by the disproportionation equilibrium 2Mnoct3+⇄Mnoct4++ Mnoct2+. This model also explains the electrical behavior of NiMn2O4 and CuMn2O4.
173 citations
TL;DR: In this paper, the electrical conductivity and thermoelectric power of single-crystalline Ba0.03Sr0.97TiO3 were measured over a wide temperature (800° to 1100°C) and oxygen partial pressure (105 to 10-15 Pa) range.
Abstract: The electrical conductivity and thermoelectric power of single-crystalline Ba0.03Sr0.97TiO3 were measured over a wide temperature (800° to 1100°C) and oxygen partial pressure (105 to 10-15 Pa) range. Our experimental data, like those of previous workers on nominally undoped BaTiO3 or SrTiO3, support a defect model based on doubly ionized oxygen vacancies, electrons, holes, and accidental acceptor impurities. The simultaneous measurement of electrical conductivity and thermoelectric power, together with precise experimental data obtained with an advanced thermoectric power measurement technique, enabled us to determine for the first time reliable values for the preexponential factors and the activation energies which characterize the defect equilibrium constants. These calculated values, together with the defect model, were found to give an excellent fit to the experimental data, and were used to generate the boundaries, in Po2-1/T space, of the various defect regimes.
143 citations
TL;DR: In this paper, the Anderson lattice model for six-fold degenerate Ce ions is used to evaluate electrical resistivity, thermoelectric power, Lorenz number and a.c. conductivity.
Abstract: Transport properties including electrical resistivity, thermoelectric power, Lorenz number and a.c. conductivity are evaluated in an approximate fashion for the Anderson lattice model for six-fold degenerate Ce ions. Coherence (Bloch's theorem) is explicitly included while the effects of intersite interactions which may be responsible for magnetic and superconducting instabilities are neglected. The calculations utilize the AverageT-matrix Approximation (ATA) with the self-consistent Non-Crossing Approximation (NCA) perturbation theory employed to give the single siteT-matrix estimate. The resistivity peaks near the characteristic Kondo temperatureT0, with high temperature logarithmic decrease and low temperatureT2 behavior. The thermoelectric power is positive and similar to the impurity result except for low temperatures; sign changes in the thermopower are in principle possible with momentum dependent hybridization. Frequency and temperature dependent optical conductivity calculations are in qualitative agreement with experimental data, although a suitably defined optical effective mass and scattering rate do not agree at least for large orbital degeneracy. The behavior of these latter quantities is qualitatively different for twofold degeneracy. Unanswered questions arising from the experimental literature are summarized.
95 citations
TL;DR: In this paper, the electrical conductivity and absolute thermoelectric power of polypyrrole have been measured between approximately 4 K and 350 K. The Mott variable-range hopping model for electrical conductivities is obeyed at higher temperatures for both types.
93 citations
TL;DR: In single crystals the authors find that the thermopOWER in the Cu-O planes is negative, while the perpendicular thermopower is positive, and measure a field-independent thermopowers to 30 T.
Abstract: Measurements of the thermopower of the high-temperature superconductor ceramics in the normal state have generally shown a positive, almost temperature-independent Seebeck coefficient, which has been interpreted by several authors in terms of the correlated hopping of the carriers as would be found in the strong Coulomb interaction limit of the Hubbard model. In this case the thermopower has a contribution from spin entropy which can be quenched by a large magnetic field. On the contrary we measure a field-independent thermopower to 30 T. Moreover, in single crystals we find that the thermopower in the Cu-O planes is negative, while the perpendicular thermopower is positive.
79 citations
TL;DR: In this paper, the Seebeck coefficient is obtained from the slope of the V(T) vs T curve, which offers simplicity of sample handling and minimal operator involvement, and can be applied to short rod-shaped samples up to a maximum temperature of 1000 C.
Abstract: The integral method of measuring the Seebeck voltage, V(T), has been applied to short rod-shaped samples. In the present method, one end of the sample is held at a fixed temperature and the other end is automatically varied through a temperature T range of interest, up to a maximum temperature of 1000 C. The Seebeck coefficient is then obtained from the slope of the V(T) vs T curve. The method offers simplicity of sample handling and minimal operator involvement.
66 citations
TL;DR: In this article, a misfit layer structure consisting of two-atom thick layers of SnS with distorted NaCl type structure and three-atom-thick sandwiches of NbS2 was described.
63 citations
TL;DR: The c-axis conductivity and TEP are suggestive of non-band-transport as might be displayed by a localized system.
Abstract: Thermoelectric power (TEP) and electrical conductivity measurements are reported for different crystal directions and for varying oxygen deficiency in single-crystal YBa/sub 2/Cu/sub 3/O/sub y/. The dependency of the transport parameters on direction are compared with the predictions of band theory. The c-axis conductivity and TEP are suggestive of non-band-transport as might be displayed by a localized system.
62 citations
TL;DR: In this paper, the authors investigated the electrical properties and its relationship to the crystal structure of La 2− x Sr x CoO 4 and showed that the Co-O-Co bond length on the perovskite-like a t − a t plane decreased and the c t / a t ratio increased with increasing Sr content.
57 citations
TL;DR: In this paper, the Seebeck coefficient in the temperature interval 300 to 1250 K has been reported for Lanthanum and transition metal mixed oxides and it has been concluded that native defects are mainly responsible for electrical conduction in these solids.
Abstract: Lanthanum and transition metal mixed oxides form an interesting series of compounds with a general formula LaMO3 (with M = Ti, V, Mn, Cr, Co, Ni and Fe). These compounds have been investigated by many workers as regards to their various physical parameters including the electrical conductivity. The new data reported in this paper refer to the Seebeck coefficient (S) in the temperature interval 300 to 1250 K. Electrical conductivity as a function of temperature has also been reported in the same temperature range and this is quite consistent with the values reported in the literature. Using these and other relevant data reported in the literature it has been concluded that native defects are mainly responsible for the electrical conduction in these solids. The nature of defect centres, charge carrier and their electrical transport mechanism is briefly discussed.
56 citations
TL;DR: In this article, the thermoelectric power of organic superconductors, β-(BEDT-TTF) 2 I 3 and β-(TTF)-TTF: bis(ethylenedithio)-tetrathiafulvalene) is calculated by the integration of the Boltzmann equation on the basis of two-dimensional tight-binding band models.
Abstract: Thermoelectric power of organic superconductors, β-(BEDT-TTF) 2 I 3 and (BEDT-TTF) 2 Cu(NCS) 2 (BEDT-TTF: bis(ethylenedithio)-tetrathiafulvalene) is calculated by the integration of the Boltzmann equation on the basis of the two-dimensional tight-binding band models. This calculation provides the interpretation of the observed complicated temperature dependence and anisotropy of the thermoelectric power and a tool estimating the transfer integrals.
TL;DR: In this paper, the Seebeck coefficient and electrical resistivity have been measured for the La3−x Mx S4 alloys with the Th3 P4 ‐type structure for M=Sm, Eu, Yb, and x=0.9 in order to determine their potential as high temperature thermoelectric energy conversion materials.
Abstract: The Seebeck coefficient and electrical resistivity have been measured for the La3−x Mx S4 alloys with the Th3 P4 ‐type structure for M=Sm, Eu, Yb, and x=0.1 to 0.9 in order to determine their potential as high‐temperature thermoelectric energy conversion materials. An analysis of the lattice parameters of these alloys suggests that Sm has a valence of 2.2 over the entire composition range. Furthermore, the variation of the Seebeck coefficient and electrical resistivity as a function of electron concentration is different for the Sm‐doped alloys than for the Eu‐ and Yb‐doped alloys, which are all different from that of the pure binary LaSy alloys. A maximum in the electrical power factor at 1000 °C is found to occur at x ≂ 0.3, but when a reasonable estimate is made of the thermal conductivity the maximum in the figure‐of‐merit at 1000 °C shifts to larger x values (∼0.7) in all alloy systems. The long term stability of the Sm and Eu ternaries is also reported.
TL;DR: In this paper, the authors presented schematic energy band diagrams for the genesis of charge carriers in non-metallic rare-earth solids, and showed that positions of 4f bands have significant effect on the genesis and nature of charge carrier, their conduction mechanism and magnitude of electrical conductivity.
Abstract: Schematic energy band diagrams for the genesis of charge carriers in non-metallic rare-earth solids have been presented. It has been shown that positions of 4f bands have significant effect on the genesis and nature of charge carriers, their conduction mechanism and magnitude of electrical conductivity (σ) and Seebeck coefficient (S) of the solid. Relevant relations have been given for bothσ and S in different situations. Experimental data on rare-earth sesquioxides (R2O3), rare-earth tungstates [R2(WO4)3] and rare-earth molybdates [R2(MoO4)3] in the intrinsic range have been explained as examples for the validity of energy band diagrams.
TL;DR: In this article, four-probe resistivity (ρ) and thermoelectric power (TEP) measurements were carried out on samples of YBa2Cu3O7−δ up to 950°C, in air and in flowing oxygen at 1 bar.
Abstract: Four-probe resistivity (ρ) and thermoelectric power (TEP) measurements were carried out on samples of YBa2Cu3O7−δ up to 950°C, in air and in flowing oxygen at 1 bar. Below 700 K the TEP is small and increases rapidly above it, reaching, at 1200 K, +140μV/K in air and +120μV/K in oxygen. At the changeover temperature (700 K) the slope of logρ vs.T changes abruptly. These results are interpreted in terms of a model of transport of carriers in a narrow band, which is full forδ = 1 and half-filled forδ = 0. Possible origins for such a narrow band are discussed in detail.
TL;DR: In this article, a powder X-ray diffraction was performed on AgNiO2 and showed that the compound has the delafossite structure of space group R 3m. Magnetic data gave evidence for the localization of the 3d-electrons of most Ni atoms.
TL;DR: In this paper, the electrical properties, conductivity and thermoelectric power of perovskites LnWOxN3−x were compared to those of oxygen tungsten bronzes and differences are explained by the nature of the elements on the anionic sites and by structural considerations.
TL;DR: In this article, anomalous scattering of the conduction holes associated with the magnetic scattering by the Cu spins was suggested as the cause of the thermoelectric powers of YBa2Cu3O7-δ and (La1-xSrx)2CuO4 single crystals.
TL;DR: The synthesis, characterization and electrical properties of representative members of the metal-rich ternary system of shandite-parkerite phases, A 2 M 3 Ch 2 and solid solutions at the A site were reported in this article.
Abstract: The synthesis, characterization and electrical properties are reported of representative members of the metal-rich ternary system of shandite-parkerite phases, A 2 M 3 Ch 2 and solid solutions at the A site. Typical metallic behaviour is exhibited by all the phases. Analysis of the Seebeck coefficients and resistivity data indicate that the rhodium and palladium containing compounds are broad band metals. Sn 2 Co 3 S 2 exhibits a phase transition below 150 K, possibly magnetic.
TL;DR: In this article, the authors measured the temperature dependences of the resistivity and thermoelectric power in YBa 2 Cu 3 O x samples with different oxygen content (6.0 ⩽ x⩽ 6.94) and provided an interpretation of experimental data based on the assumption of the charge carrier density of states containing a narrow peak located near the Fermi level.
TL;DR: In this article, the thermoelectric power of Y1Ba2Cu3O7−y has been precisely measured in absence of, but also under applied (small) magnetic fields over a large temperature range [65 −230 K].
TL;DR: In this article, the normal state transport properties of sintered samples of YBa2Cu3O7- delta as a function of temperature and at pressures up to 8 kbar were measured.
Abstract: The authors have measured the normal-state transport properties of sintered samples of YBa2Cu3O7- delta as a function of temperature and at pressures up to 8 kbar. The room-temperature resistivity decreases at -1.0% kbar-1. The Hall coefficient has a value of 2.8*10-9 m3 C-1 at room temperature, rising to 7.8*10-9 m3 C-1 just above the superconducting transition temperature. This gives an effective carrier concentration of 0.4 holes per unit cell at room temperature. In contrast to the strong temperature dependence of RH, the pressure dependence is very weak ( mod dRH/dP mod <1% kbar-1) and they show that this is inconsistent with the temperature dependence if we assume a simple volume dependence of RH. They discuss models for the Hall coefficient and consider that its temperature dependence is determined by the low-dimensional character of the energy bands near the Fermi energy.
TL;DR: In this paper, it was shown that there is some merit in using a material with a low Seebeck coefficient, but with a very high ratio of electrical conductivity to thermal conductivity as the positive branch.
Abstract: The figure of merit for energy conversion by a thermocouple involves a combination of the properties of the two branches. Although it often has a value that is close to the average of the branch figures of merit, this is not always the case. In particular, there is no positive thermo-electric material that matches the negative thermo-elements, made from bismuth-antimony, that are useful at low temperatures. It is shown that there is some merit in using a material with a very low Seebeck coefficient, but with a very high ratio of electrical conductivity to thermal conductivity as the positive branch. Consideration is given to the use of the new high-temperature superconductors for this purpose. Experiments on the latter in a magnetic field at liquid-nitrogen temperature are reported.
TL;DR: In this paper, the thermoelectric power of iron-carbon alloys and its variations due to carbide precipitation are studied and analyzed and it is shown that carbon in solid solution decreases the T.E. of iron by reducing the lattice component.
TL;DR: In this paper, the activation energy for the diffusion of oxygen varies between 0.82 and 0.92 eV, depending on the degree of oxidation, for the fast oxidation process of YBa 2 Cu 3 O x.
TL;DR: Measurements of the thermoelectric power of the high-temperature Tl-Ca-Ba-Cu-O superconductor indicate a transition which is centered at 118 +- 3 K, in agreement with magnetic measurements and published resistivity results.
Abstract: We report measurements of the thermoelectric power of the high-temperature Tl-Ca-Ba-Cu-O superconductor. The data indicate a transition which is centered at 118 +- 3 K, in agreement with magnetic measurements and published resistivity results. The thermoelectric power is positive and, aside from the high transition temperature, is remarkably similar in magnitude and temperature dependence to that of the rare-earth-based oxide superconductors which have been reported previously.
Abstract: The measurement of DC electrical conductivity and thermoelectric power of the bulk samples of chalcogenide glasses of the system Se70Te30, Se70Te30−xInx (x = 1, 3, 5, 7, 9% atomic weight) are studied. The activation energies are obtained from conductivity and thermoelectric power measurements, using Mott, Davis and Fritzsche equations. The difference of activation energies E Q = E σ ∗ − E s ∗ = 0.12 eV is explained on the basis of long range electrostatic potential fluctuations, and this difference in activation energies is in agreement with the results reported by Overhof and Beyer for the chalcogenides. And it has also been observed that addition of indium in the samples increases the electrical conductivity.
TL;DR: In this article, the Seebeck effect or thermoelectric power of granular ceramic oxide superconductors in an effective medium approximation was discussed and experimental results were compared to the theory.
TL;DR: The temperature dependence of rho, together with Hall effect and thermoelectric power measurements, suggests hopping conduction between localized states at low temperatures, with diffusive transport at higher temperatures.
Abstract: We have measured resistivity rho components both parallel and perpendicular to the Cu-O planes in single-crystalline La/sub 2/CuO/sub 4/. Substantial anisotropy, reaching values as large as 10/sup 3/, is observed in the resistivity. The temperature dependence of rho, together with Hall effect and thermoelectric power measurements, suggests hopping conduction between localized states at low temperatures, with diffusive transport at higher temperatures. These results are in contradistinction to previous reports.
TL;DR: In this paper, the authors measured the thermoelectric power of single phase YBa2Cu3O7−x superconductors in the temperature range 4.2-300K.