Showing papers on "Seebeck coefficient published in 1987"
TL;DR: In this article, the effects of different cation substituents on electric and thermal transport in YCrO/sub 3/ and LaCrO / sub 3/ were investigated.
Abstract: High-temperature electrical conductivity, Seebeck coefficient, and thermal conductivity measurements were used to study the effects of different cation substituents on electric and thermal transport in YCrO/sub 3/ and LaCrO/sub 3/. The substitution of divalent Ca and Sr for Y and La, respectively, resulted in the formation of small polarons as charged carriers. The additional substitution of Mn for Cr resulted in the formation of a second charge carrier associated with the Mn. The electrical conductivity results were consistent with thermally activated transport by hopping of a temperature-independent carrier concentration. The activation energies were 0.20 and 0.12 eV for (Y,Ca)CrO/sub 3/ and (La,Sr)CrO/sub 3/, respectively, and increased to about 0.50 eV with the substitution of Mn for Cr. The Seebeck coefficient increased linearly with temperature and decreased with substituent concentration for both (Y,Ca)CrO/sub 3/ and (La,Sr)CrO/sub 3/. The substitution of Mn for Cr resulted in a Seebeck coefficient with a more complex dependence on temperature and substituent concentration. The thermal conductivity did not change significantly with either cation substitution or temperature.
162 citations
TL;DR: In this article, the magnetic properties of the heavy fermion state of CeCu 6 were investigated and the Hall coefficient was found to be almost independent of the cerium concentration.
130 citations
TL;DR: Thermoelectric power measurements are reported in some La/sub 2/CuO/sub 4-//sub y/ oxides with Ba and Sr doping, and the temperature dependences found indicate that the materials are not simple, uncorrelated wide-band metals.
Abstract: Thermoelectric power (S) measurements are reported in some La/sub 2/CuO/sub 4-//sub y/ oxides with Ba and Sr doping. S gradually decreases with increasing dopant concentration x, and for small concentration the trend can be described by assuming strong correlations. While S is small for high x, the temperature dependences found indicate that the materials are not simple, uncorrelated wide-band metals.
112 citations
TL;DR: In this paper, it was shown that the change in conduction type is not related to the relative drift mobilities of electrons and holes, but to the shift of the Fermi level toward the conduction band.
Abstract: The electrical properties such as thermoelectric power, electrical conductivity and drift mobility have been studied on the chalcogenide glasses in the system Pb-Ge-Se. It has been found that the glasses in a certain composition range exhibit n-type conduction, as the second case in chalcogenide glasses, following the Bi-containing glasses. There were little differences in the electron and hole drift mobilities in a given glass, regardless of its conduction type. Above finding implies that the change in conduction type is not related to the relative drift mobilities of electrons and holes, but to the shift of the Fermi level toward the conduction band. The appearance of n-type conduction has been discussed in terms of chemical bonds.
75 citations
TL;DR: In this article, the Hall coefficient is shown to vary with T-1.2 K ≤ T ≤ 120 K. The thermopower is very small and sample dependent, and the thermal conductivity indicates dominant phonon heat transport in more than one band.
Abstract: For the high-Tc superconductor YBa2Cu3O7, we present results on the resistivity, Hall effect, and thermopower for temperatures up to 350 K as well as on the thermal conductivity in the range 0.2 K ≤ T ≤ 120 K. The Hall coefficient is positive and varies approximately with T-1. The thermopower is very small and sample dependent. These results suggest transport in more than one band. The thermal conductivity indicates dominant phonon heat transport. For the residual resistivity an upper bound, ρ0 ≤ 250 μΩ cm, is deduced. Combining this with published results for the slope of the upper critical field and the penetration depth, we estimate the specific-heat coefficient, 5 ≤ γ < 9 mJ/K2 mole-Cu, and the effective carrier density, 1.1 1022 cm-3.
73 citations
TL;DR: In this paper, the maximum conductivity of PT-FeCl 4 -films was observed to be 50 Scm −1 which corresponds to a maximum dopant concentration of approximately 26 mol-%.
70 citations
TL;DR: The electrical resistivity and the Seebeck coefficient of thermally evaporated thin bismuth films of thicknesses from 300 to 1900 A\r{} have been measured and the latter is negative and its magnitude is found to increase initially with increasing temperature, reach a maximum, and then decrease with a further rise in temperature.
Abstract: The electrical resistivity and the Seebeck coefficient of thermally evaporated thin bismuth films of thicknesses from 300 to 1900 A\r{} have been measured in the temperature range 300--470 K. The latter is negative and its magnitude is found to increase initially with increasing temperature, reach a maximum, and then decrease with a further rise in temperature. The temperature at which the Seebeck coefficient is maximum is found to be thickness dependent, decreasing with increasing thickness. The observed dependence is explained by considering that the Fermi energy is temperature dependent. Bismuth films show a negative temperature coefficient of resistivity. The thickness dependence of the electrical resistivity and the Seebeck coefficient of simultaneously prepared films are analyzed using the newer effective mean-free-path model. From the analysis, important material constants like the mean free path, the electron concentration, and the effective mass of electrons have been evaluated.
69 citations
TL;DR: A large positive peak at a temperature of more than twice the respective superconducting transition temperature suggests a strong phonon-drag contribution to the thermopower and a positive Hall coefficient combined with a negative diffusion thermopowers implies the presence of more more than one type of carrier.
Abstract: The thermoelectric power, Hall coefficient, and resistivity have been measured on two samples of ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}$ with a strontium content of $x=0.2$ and $x=0.25$. We observe typical metallic behavior with a strong electron-phonon interaction and a low density of carriers. A large positive peak at a temperature of more than twice the respective superconducting transition temperature suggests a strong phonon-drag contribution to the thermopower. At higher temperatures the thermopower changes sign from positive to negative, a trend that increases with increasing Sr content. A positive Hall coefficient combined with a negative diffusion thermopower implies the presence of more than one type of carrier.
67 citations
TL;DR: In this paper, the electronic conductivity and thermoelectric power of a magnetic ferrite of composition Mn0.863Fe2 have been measured as functions of oxygen partial pressure and temperature.
Abstract: The electronic conductivity and thermoelectric power of a magnetic ferrite of composition Mn0.863Fe2.137O4 have been measured as functions of oxygen partial pressure and temperature. Within the single-phase region of the spinel ferrite, both electrical properties are essentially independent of the oxygen partial pressure, implying that the electronic charge carrier concentration is governed by the molecularity rather than by oxygen nonstoichiometry. The electrical conduction behavior is successfully interpreted on the basis of a small polaron model, yielding a hopping energy of 0.363 ± 0.008 eV and a drift mobility of 0.05 to 0.10 cm2/(V·s) in the temperature range of 900 to 1300 K.
62 citations
TL;DR: In this paper, the results of electrical conductivity and thermoelectric studies on antimony telluride in the thin film state were reported, where vacuum-deposited on to clean glass substrates with thickness between 50 and 200 nm and studied in the temperature interval 300 to 470 K. This is attributed to an amorphous to crystalline transition, which is confirmed by X-ray diffractogram and electron diffraction patterns.
Abstract: The results of electrical conductivity and thermoelectric studies on antimony telluride, a promising thermoelectric material, in the thin film state are reported. Films were vacuum-deposited on to clean glass substrates with thickness between 50 and 200 nm and studied in the temperature interval 300 to 470 K. On heating the as-grown films, there is a sharp fall both in the Seebeck coefficient and the electrical resistivity at around 340 to 370 K for all the films. This is attributed to an amorphous to crystalline transition, which is confirmed by X-ray diffractogram and electron diffraction patterns.[/p]
45 citations
TL;DR: In this article, electrical resistivity and thermoelectric power were measured for La{sub 2}CuO{sub 4y} with Ba and Sr-doping, and surface impedance measurements at 102 GHz were used to determine the magnitude and temperature dependence of the gaps in the Ba-doped materials.
Abstract: High T{sub c} superconducting oxides have been prepared by the amorphous citrate process. The resulting powders require less high temperature processing than standard techniques and lead to sintered compacts with over 90% density. Electrical resistivity and thermoelectric power were measured for La{sub 2}CuO{sub 4-y} with Ba and Sr-doping. The addition of dopants decreases the thermopower and there is the suggestion that strong correlations may be occurring at small dopant concentrations. Surface impedance measurements at 102 GHz have been used to determine the magnitude and temperature dependence of the gaps in the Ba-doped materials.
TL;DR: In this article, the electrical properties of La2NiO4 have been studied with respect to the stoichiometry of the material and the results are well described within the frame of variable range hopping.
TL;DR: The phthalocyanine molecular metal Ni(Pc) (C104)y, y=0.39−0.47 for most crystals, has been synthesized by electrocrystallization techniques.
TL;DR: In this article, the dc-conductivity and thermoelectric pover of electrochemically prepared polypyrroles have been investigated in the temperature range between 300 K and 1.3 K on unaged.
TL;DR: The new germanium-rich manganese germanide, Mn3Ge5, was synthesized at 600-1000°C and 4 GPa using a Belt-type apparatus.
TL;DR: In this article, the temperature dependence of the thermopower is modified by the electron-phonon interaction, and an unexpected precursor effect just above the transition temperture Tc is found.
Abstract: The recent discovery of high-temperature oxide superconductors1–4 has generated enormous interest both among physicists and, because of their obvious technological importance, in the wider community. One of the less-studied but potentially interesting properties is the thermoelectric power (or thermopower), which is the coefficient that characterizes the electromotive force resulting from the redistribution of electrons in a temperature gradient. The temperature dependence of the thermopower is modified by the electron-phonon interaction, and provides a means of estimating the strength of the interaction. We have performed measurements on several samples of YBa2Cu3O7–δ, and find an unexpected precursor effect just above the transition temperture Tc—namely, an increase rather than decrease in thermopower. The measured thermopower is positive with a magnitude typical of metallic conductors, and shows some similarity to the calculated diffusion thermopower for a reltively large electron-phonon coupling parameter of λ≈ 2.5.
TL;DR: In this article, the thermoelectric power of the magnetically ordered Kondo lattices CeCu2Ge2, CeCu4Al8 and CePb3 was measured up to 350 K and compared with that of heavy-fermion UBe13.
TL;DR: In this article, the electrical conductivity, its temperature coefficient and the thermoelectric power of Bi 1− x Sb x films with 0 x ⩽ 0.3 and thickness from 20 to 400 nm were measured in the temperature range 80 −400 K.
TL;DR: In this paper, the annealing of several samples in the temperature range of 1100-1300 C resulted in the power factor P (= S-squared/rho) increasing with increased annesaling temperature, suggesting that other changes besides that in the carrier concentration took place.
Abstract: Silicon-germanium alloys doped with GaP are used for thermoelectric energy conversion in the temperature range 300-1000 C. The conversion efficiency depends on Z = S-squared/rho lambda, a material's parameter (the figure of merit), where S is the Seebeck coefficient, rho is the electrical resistivity and lambda is the thermal conductivity. The annealing of several samples in the temperature range of 1100-1300 C resulted in the power factor P (= S-squared/rho) increasing with increased annealing temperature. This increase in P was due to a decrease in rho which was not completely offset by a drop in S-squared suggesting that other changes besides that in the carrier concentration took place. SEM and EDX analysis of the samples indicated the formation of a Ga-P-Ge rich phase as a result of the annealing. It is speculated that this phase is associated with the improved properties. Several reasons which could account for the improvement in the power factor of annealed GaP doped SiGe are given.
TL;DR: In this article, the influence of iodine on the electrical conductivity and thermoelectric power of lead phthalocyanine thin films and pressed samples was investigated and a compensation rule for the conductivity is also valid.
TL;DR: Boron carbides exhibit an anomalously large Seebeck coefficient with a temperature coefficient that is characteristic of polaronic hopping between inequivalent sites, which is associated with disorder in the solid as mentioned in this paper.
Abstract: Boron carbides exhibit an anomalously large Seebeck coefficient with a temperature coefficient that is characteristic of polaronic hopping between inequivalent sites. The inequivalence in the sites is associated with disorder in the solid. The temperature dependence of the Seebeck coefficient for materials prepared by different techniques provides insight into the nature of the disorder.
TL;DR: In this paper, the use of high-Tc superconductors for precision determination of the absolute thermoelectric power is illustrated on commercially available wires of copper and Nb•Ti.
Abstract: The use of the recently discovered high‐Tc superconductors for purposes of precision determination of the absolute thermoelectric power is illustrated on commercially available wires of copper and Nb‐Ti. High‐Tc superconductors offer a wide range of temperatures where precision metrology can be carried out, and their unusually steep upper critical field allows for an accurate determination of the effect of magnetic field on the thermopower of test leads.
TL;DR: In this paper, thermal and electrical resistivity measurements were made for the mixed inverse system CuxCo1−xFe2O4 with x = 0, 0.75, and 1.21 eV.
Abstract: Thermoelectric power (α) and electrical resistivity (ϱ) measurements are made for the mixed inverse system CuxCo1−xFe2O4 with x = 0, 0.25, 0.5, 0.75, and 1. The measurements are done from room temperature up to 600 K. It is found that all samples are n-type semiconductors with activation energy varying from 0.59 to 0.21 eV for different samples. The activation energy plot shows a maximum at x = 0.5. The drift mobility of charge carriers (μd) is calculated at different temperatures. From the values of μd and the temperature dependence of both, (α) and (ϱ) it is suggested that the transport properties measured may be interpreted using the localized model of electron (polarons).
TL;DR: In this article, the effect of Coulomb interaction with the single-orbital Anderson model on the thermoelectric power of a dilute impurity system was investigated with the use of the Bethe-Ansatz solution of the Anderson model.
Abstract: The thermoelectric power for the dilute impurity system is calculated at low temperatures by means of the Bethe-Ansatz solution of the Anderson model. The effect of the Coulomb interaction is investigated with the use of the single-orbital Anderson model. The orbitally degenerate case is investigated as well with the use of the highly correlated model adequate for the Ce(Yb) impurity system. The giant thermoelectric power is discussed with the results obtained for the enhancement factor and the renormalized f -level position.
TL;DR: The results of a study of the thermal conductivity, electrical resistivity, and Seebeck coefficient of Ni3Al are described in this article, where it is shown that phonon conduction is an important part of thermal conductivities.
Abstract: The results of a study of the thermal conductivity, electrical resistivity, and Seebeck coefficient of Ni3Al are described. The thermal and electrical conductivities are sensitive to composition and attain their maximum values in well‐ordered, stoichiometric Ni3Al. Nonstoichiometry (antisite defects), and Fe (a substitutional solute) and B (an interstitial solute) contents are all about equally effective in reducing the transport properties. Even for stoichiometric Ni3Al, the temperature variation of the thermal and electrical conductivities resembles that of an alloy, and this is attributed to scattering associated with the loss of ferromagnetic order at ∼60 K. Experimental data and a theoretical analysis show that phonon conduction is an important part of the thermal conductivity and not very sensitive to composition or stoichiometry.
TL;DR: In this paper, the transport and magnetic properties of the (La1-xAx)2CuO4 system are investigated systematically over the composition range from x = 0 to 0.1.
Abstract: The transport and magnetic properties of the (La1–xAx)2CuO4 system are investigated systematically over the composition range from x = 0 to 0.1. The change in the resistivity and magnetic susceptibility with alkaline metals and alkali earth metals substitution seems to be consistent with the band picture with nesting Fermi surface. However, the result for the Seebeck coefficient suggests the possibility of a strongly correlated electron system, casting a question about the simple SDW picture. The similar feature in the Seebeck coefficient is also observed in the Ba2YCu3O7-y system.
TL;DR: In this article, the authors present the results of thermogravimetric, electrical conductivity and thermoelectric power measurements for a manganese bronze, Na 0.7 MnO 2, under the conditions of thermodynamic equilibrium (600-1000 K) and at quenched defect structure.
TL;DR: The temperature dependence of the thermoelectric powers of the high-temperature oxide superconductors Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-//sub x/ and (Eu-Y) is reported.
Abstract: The temperature dependence of the thermoelectric powers of the high-temperature oxide superconductors Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-//sub x/ and (Eu-Y)/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-//sub x/ is reported. The sign of the dominant carriers in the normal state is observed to be positive. Well above the superconducting transition, the magnitude of the thermoelectric power is a weakly decreasing function of temperature.