Showing papers on "Seebeck coefficient published in 1986"

Multichannel Landauer formula for thermoelectric transport with application to thermopower near the mobility edge

Abstract: Various thermoelectric linear transport coefficients are defined and calculated for two reservoirs connected with ideal multichannel leads and a segment of an arbitrary disordered system. The reservoirs have different temperatures and chemical potentials. All of the inelastic scattering (and, thus, the dissipation) is assumed to occur only in the reservoirs. The definitions of the chemical potentials and temperature differences across the sample itself (mostly due to elastic scattering) are presented. Subtleties of the thermoelectric effects across the sample are discussed. The associated transport coefficients display deviations from the Onsager relations and from the Cutler-Mott formula for the thermopower (although the deviations vanish for a large number of channels and/or high resistance). The expression obtained is used to predict the critical behavior of the electronic thermopower near the mobility edge. It is shown to satisfy a scaling form in the temperature and separation from the mobility edge.

Thermodynamic and transport properties of UPt3

Abstract: In the normal phase of UPt3, the magnetoresistivity is large and positive with the striking feature of a quasi-independence of the temperature and magnetic field terms; the thermoelectric power has aT 2 dependence and the susceptibility is almost constant up to 4 K. The superconducting transition is broadened and the specific heat jump is weak due to the strong anisotropy of its normal phase. FromT c to 146 mK (the lowest experimental temperature), a largeT 2 contribution is observed in the specific heat, but the thermal conductivity has the same dependence only below 150 mK. These results are compared with the predictions given for polar odd-pairing superconductivity.

Electrical conductivity and thermoelectric power measurements of some lithium–titanium ferrites

Abstract: The electrical conductivity and thermoelectric power of some lithium–titanium ferrites with small amounts of manganese and zinc have been studied as a function of temperature in the range of 300–550 K and are reported here. The conductivity variation shows two different regions with a large variation in the activation energies. The possible mechanisms with respect to ionic conduction and electron hopping are discussed with the support of thermoelectric power measurements. Lattice parameters are also calculated from x‐ray diffractograms for confirming the single‐phase nature of the ferrites.

Electrical conduction and effective mass of a hole in single-crystal NiO

Abstract: The electrical conductivity and Seebeck coefficient of single-crystal NiO were measured at 1100 to 1400° C. The activation energies for conductivity and thermoelectric power were 84.1 and 76.5 kJ mol−1, respectively, which was interpreted as showing band-like conduction occurring at high temperatures. Doubly ionized cation vacancies were believed to be the dominant point defects, and the impurity effect gave rise to a $$P_{{\text{O}}_{\text{2}} }^{1/5} $$ dependence of conductivity. The effective mass of a hole, m *, was calculated based on a band-conduction scheme using the literature value of the deviation from stoichiometry, δ, and the hole mobility μ. The value of m * was in the range 0.8 to 1.0m 0, and slightly decreased with increasing temperature.

Electronic transport properties in conducting Langmuir-Blodgett films

Abstract: Conducting Langmuir-Blodgett (LB) films made of a ternary compound N-docosylpyridinium-tetracyanoquinodimethane-iodine have been recently obtained by Ruaudel and co-workers (1985), after an in-situ oxidation of a precursor LB film. This paper describes a new well controlled method used to perform the iodine 'doping' in the precursor LB film. The chemical reactions involved in this process are followed by UV-visible spectroscopy. Direct current and microwave conductivities of samples obtained in that way have both been measured in the range 300-120 K and are correctly fitted by the relation sigma = sigma 0 exp - Delta E/kT with two different activation energies: 0.15 eV and about 0.08 eV respectively. Thermoelectric power measurements have also been performed in the range 298-176 K and the Seebeck coefficient, the value of which is 26 mu V K-1 at room temperature, exhibits a linear-like behavior against 1/T with a slope dS/d(1/T) approximately=11 mV. All these measurements suggest a semiconducting behavior and are tentatively analysed in terms of an intrinsic semiconductor model. However, as an important discrepancy about the mobility value appears, the authors suggest a presumable interpretation in terms of hopping model between localised states. But they conclude that more precise information about the inplane molecular arrangement and the carrier density is needed to provide a more coherent model for the transport properties in these conducting films.

The Optical Interband Transitions of the Semiconductor CuGaO2

Abstract: Determination des transitions optiques interbande et de la position du bord de la bande de valence d'apres des mesures de l'effet photoelectrochimique

Electrical and optical properties of amorphous SixN1−x

Abstract: Amorphous silicon nitride films have been prepared by the glow-discharge decomposition of a wide range of ammonia/silane gas mixtures. In particular, samples prepared from mixtures containing very small amounts of ammonia have been investigated. The dark- and photoconductivities, the optical gap and the thermoelectric power have been measured as a function of the volume ratio of the deposition gases, denoted by R. A range of specimens has also been prepared in a junction configuration, and the electron and hole mobilities of these has been determined. The results of all of the measurements show a systematic and continuous variation with R. Extended-state conduction predominates throughout, and the majority carriers are electrons. For R < 5 × 10−3 it is believed that a shallow level of ionized donor states is introduced. This is supported by the sensitization of the photoresponse, the decrease in the conductivity activation energy and the decrease in the electron drift mobility activation energy. ...

Influence of process conditions on the electrical and optical properties of RF magnetron sputtered MoS2 films

Abstract: Electrical transport and optical properties of magnetron sputtered MoS2 films have been investigated as a function of process conditions. The results for the as-sputtered films and the influence of thermal annealing have been discussed in relation to the specific film morphologies and their inherent grain boundaries. Electrical resistivity measurements (300-10K) have shown that the substrate temperature (Ts) is the dominant sputtering parameter. At room temperature the resistivity varied between 3.8*10-2 Omega cm (Ts=-70 degrees C) and 10.1 Omega cm (Ts=150 degrees C). Hall effect measurements indicated very low Hall mobilities (1-5 cm2 V-1 s-1 at 297K). A check of the thermoelectric power response showed that for both the as-sputtered and annealed films the majority charge carriers are electrons. From optical absorption measurements an energy gap of 1.17 eV has been determined. In contrast to the electrical transport results, the optical properties were weakly influenced by process conditions.

Metal-Insulator Transition in LixZn1-xV2O4

Abstract: Thermoelectric power and electrical resistivity were measured for sintered Li x Zn 1- x V 2 O 4 (0≤ x ≤1). From the temperature and the compositional dependences of the Seebeck coefficient, it is inferred that the metal-insulator transition occurs at 0.3< x <0.4. However, there was no abrupt change in the resistivity. To explain the temperature dependence of the Seebeck coefficient, random distribution of low excited localized states was postulated and the transition seems to be of Mott-Anderson type.

Temperature and thickness dependence of electrical and thermal transport coefficients of Bi1–xSbx films in an anisotropic, non-degenerate two-band model

Abstract: The thickness and temperature dependences of electrical and thermal transport coefficients (e.g. electrical conductivity, thermoelectric power, thermal conductivity) of Bi1–xSbx films are described by a non-degenerated two-band model, considering the anisotropic elliptical band structure (many-valley model) of bulk Bi1–xSbx. The transport coefficients are measured in the temperature range 80 to 400 K on films with thicknesses 20 to 400 nm and the results are interpreted and discussed using the deduced relations. Die Schichtdicken- und Temperatura bhangigkeit elektrischer und thermischer Transportkoeffi-zienten (z. B. der elektrischen Leitfahigkeit, der Thermokraft, der Warmeleitfahigkeit) von Bi1–xSbx-Schichten wird im Rahmen eines nicht entarteten Zweiband-Modells unter Berucksichtigung der anisotropen elliptischen Bandstruktur (many valley model) von massivem Bi1–xSbx beschrieben. Die Transportkoeff izienten werden im Temperaturbereich 80 bis 400 K an Schichten von 20 bis 400 nm Dicke gemessen, und die Ergebnisse werden mit den abgeleiteten Beziehungen interpretiert und diskutiert.

Electrical transport in heavy rare-earth vanadates

Abstract: This paper reports measurements of electrical conductivity (σ) and Seebeck coefficient (S) between 300 and 1250 K and differential thermal analysis (DTA) and thermogravimetric analysis (TGA) between 300 and 1200 K, together with X-ray diffraction studies of heavy rare-earth vanadates (RVO4 with R=Tb, Dy, Ho, Er and Yb) All these vanadates have been found to have a tetragonal unit cell The DTA study shows a flat dip in the temperature interval 1075 to 1300 K, indicating a possible structural phase transition of these compounds Practically no weight loss has been observed in TGA from 300 to 1200 K in any of the vanadates All RVO4 are semiconducting materials with the room-temperatureσ value lying in the range 10−12 to 10−3 Ω−1 m−1, becoming of the order of 10−2 Ω−1 m−1 around 1000 K The electrical conductivity of all vanadates exhibits an exponential increase in the temperature intervals 420 K toT 1 andT 1 toT 2, with different values of the activation energy A logσ againstT −1 plot shows a peak aroundT 3 and drops to a minimum value aroundT 4, before increasing again with temperatureT 4 >T 3 >T 2 >T 1 are different for different vanadates and these are termed “break temperatures”T 4 lies well within the temperature range of the DTA peak and can be termed the phase transition temperature In the lower temperature interval the electrical conduction is essentially extrinsic The localized charge carriers on defect centres conduct by a hopping mechanism The defect centres are V4+ ions in all vanadates with R4+ centres in some of them It is concluded that in the temperature intervalT 1

Electrical conductivity and thermoelectric power of nickel ferrous ferrite variable-range hopping and the Coulomb gap

Abstract: Electrical conductivity and thermoelectric power measurements have been made on single crystals of nickel ferrous ferrite, NixFe3-xO4 of compositions 0x0·9, in the temperature range 10 to 300 K. The temperature and concentration dependences of the conductivity and of the thermopower at high nickel concentrations (x  0·4) are discussed in terms of variable-range hopping and of nearest-neighbour hopping in an energy distribution of localized states, or the 'Anderson band'. It is argued that there is evidence for the formation of a Coulomb gap and for many-electron hopping in samples of low nickel content (x<0 4).

Thermoelectric voltage between identical metals in a point-contact configuration.

Abstract: In an electric circuit made from only one metal with a thermal gradient over a point contact in the chain, thermoelectric voltages emerge as a result of the finite size of the contact. The phenomenon is described in terms of the difference in the transport properties of a point contact and the bulk, yielding the phonon drag as a major contribution to the measured thermopower at temperatures T

Ni-based thermocouples in the mineral-insulated metal-sheathed format: thermoelectric instabilities to 1100 degrees C

Abstract: EMF drift and changes in Seebeck coefficient were examined in metal-sheathed Ni-based thermocouples held at temperatures in the range 500-1100 degrees C for up to 1000 h. In 200 h, EMF drifts of up to the equivalent of 10 degrees C were observed and a subsequent reduction in immersion caused a drop of 80 degrees C. The analysis of X-ray spectra showed the presence and migration of Mn to be the main contributor to instability. The most stable configuration examined was the Inconel-sheathed Nicrosil/Nisil thermocouple. It is suggested that the optimum Ni-based thermocouple is one having Nicrosil and Nisil thermoelements and a Nicrosil sheath.

Transport properties of high purity, polycrystalline titanium diboride

Abstract: Thermal conductivity data for several TiB2 samples are presented and the results for one sample extend from 80 to 400 K. These results show that the thermal conductivity attains a maximum value of about 130 W/m K at 140 K. An analysis of the results shows that this is caused by the electronic component of the thermal conductivity and that phonon conduction is also probably significant. Seebeck coefficient values agreed with the results of previous studies. The electrical resistivity of one sample was also determined to 1800 K. These results can be described by the Bloch–Gruneisen equation if the effect of thermal expansion is included.

A simple technique for determining the Seebeck coefficient of thermoelectric materials

Abstract: It is shown that the Seebeck coefficient of a semiconductor against copper can be determined in terms of that for a copper-constantan thermocouple by means of a rapid potentiometric measurement. Values obtained for typical samples of bismuth telluride alloy, using the apparatus that is described, are compared with those given by a conventional method and indicate that the technique is perfectly satisfactory.

Exhaust heat utilizing device for engine

Abstract: PURPOSE: To obtain high temperature gradient and to conduct thermoelectric generation with good efficiency by providing a thermoelectric generation element for generating thermoelectric power by Seebeck effect and disposing both ends of the element adjacent to a high temperature portion of an engine and a cooling water passage. CONSTITUTION: An annular thermoelectric generation element 8 is disposed between a water jacket 6 and a combustion chamber 7 of an engine. The thermoelectric generation element 8 is constructed so that n-type semiconductors and p-type semiconductors are alternately arranged, a high temperature side heat receiving plate 9 is joined to the inner peripheral portion thereof on the combustion chamber 7 side, a low temperature side radiating plate 10 positioned between the semiconductors and phase-to-phase insulated is joined to the outer peripheral portion thereof on the water jacket 6 side so as to obtain Seebeck effect. In this arrangement, by a temperature gradient of high temperature of the combustion chamber 7 and low temperature of the water jacket 6 during driving of an engine, the thermoelectric generation element 8 is caused to generate thermoelectric power based upon Seebeck effect. Thus a high temperature gradient can be obtained to conduct thermoelectric generation with good efficiency. COPYRIGHT: (C)1988,JPO&Japio

Thermoelectric properties of a two-dimensional electron gas exhibiting the quantum Hall effect.

Abstract: This Communication reports studies of the thermoelectric properties of a two-dimensional electron gas in the quantum Hall regime. The data are compared to theoretical predictions for the thermopower when the chemical potential lies either in the middle of a Landau level or midway between two levels. For the comparison a Gaussian broadening is assumed and a good fit to the data can be obtained with the width of the levels as the adjustable parameter.

The Hall effect in glassy and liquid metals

Abstract: It is demonstrated that the existence of positive Hall coefficients in glassy and liquid metals can in principle be explained by the Faber-Ziman theory. The theory leads to a correlation with the thermopower which is in qualitative agreement with the experimental results but which is not suitable for quantitative calculations. Suggestions for a more general approach are given.

The electrical conductivity and thermoelectric power of lithium ferrite in the vicinity of the order-disorder transition temperature

Abstract: The electrical conductivity and thermoelectric power of single crystals of lithium ferrite have been measured in the temperature range 300 to 1100 K. Discontinuous decreases in the conductivity and in the thermopower have been observed at the order-disorder temperature (1000 K). These features of the results are explained in terms of an increase in the width of the energy distribution or ‘Anderson band’ of localized states and a concomitant increase in the magnitude of the polaron binding energy.

Electrical and thermal transport properties of the Y1 − x Mx CrO3 system

Abstract: The effects of substituting divalent metal ions (Mg, Ca, Sr, Ba) for Y in YCrO3 were investigated by electrical conductivity, Seebeck coefficient, and thermal conductivity measurements. The electrical conductivity results were consistent with the hopping-type conduction of a temperature-independent concentration of small polarons, with measured activation energies of 0.18-0.26 eV. The Seebeck coefficient increased nearly linearly with temperature and indicated p-type conductivity. Both electrical conductivity and Seebeck coefficient results show a strong dependence on dopant size (ionic radius) and indicate that the highest carrier concentrations were associated with Ca as the dopant, which is attributed to the similar ionic radii of Ca2+ and Y3+. The thermal conductivity decreased slightly with temperature and dopant concentration.

Some electric properties of PLZT ceramics

Abstract: The measurement results of permittivity, loss tangent, remanent polarization and electric conductivity of Pb(Zr0.52Ti0.48)O3 ceramics with La doping up to 10% are presented. The type of electric conductivity is determined by using the Seebeck coefficient measurement method. Marked decrease of electric conductivity has been found with increasing La content as well as the change of conductivity type in samples containing more than 7% of La.

Small bipolaronic hopping in boron carbides

Abstract: D.c. conductivity, Hall mobility and Seebeck coefficient measurements on boron carbides, B1−xCx (0.1 ⩽ x ⩽ 0.2), between 300 and 1200 K are interpreted in terms on the hopping of small bipolaronic holes between B11C icosahedra that are inequivalent in energy and electron-lattice coupling strength.

Electrical Resistivity of YFe2O4

Abstract: The electrical resistivity and the Seebeck coefficient of both stoichiometric and nonstoichiometric YFe 2 O 4 were measured in the temperature range 140 to 290 K The activation type conduction was observed with the activation energy of 022 eV above T N for both oxides Below T N , the conduction in the nonstoichiometric oxide is probably due to the variable range hopping in the two dimensional lattice Resistivity of the stoichiometric oxide obeys the Hurd's model superficially However, it will not be the atomic vibration effect but would be the gap narrowing effect