Differential Thermopower Research Articles

Electron Transport Properties of Eu(Cu1 − xAgx)2Si2 (0 ≤ x ≤ 1): Initiation of Transition Eu2+ ↔ Eu2.41+ in the Intermediate Valence State

The article presents the results of studies of the chemical composition, crystal structure, lattice parameters, microstructure, the valence state of the europium ion (at 300 K), electrical resistivity, and differential thermopower (6–400 K) of samples in the Eu(Cu1 − xAgx)2Si2 (0 ≤ x ≤ 1) substitutional solid solutions. A transition of the europium ion from the valence-stable state of Eu2+ in EuAg2Si2 to the state of intermediate (homogeneous) valence (IV) of the europium ion in EuCu2Si2 with an effective valence ϑeff = 2.41 (300 K) has been initiated by a successive replacement of silver atoms by copper atoms. With appropriate sample compositions, the transition passes through a Kondo-type state. The research subject is the patterns of transformations (when the composition of the sample changes), the electronic state, and, accordingly, the electronic transport properties. The simultaneous coexistence of europium ions in different electronic states is assumed. The substitutional solid solution Eu(Cu1 − xAgx)2Si2 (0 ≤ x ≤ 1) exhibits properties related to the competition between the state of the Kondo system, intermediate valence (IV), and magnetic ordering.

Two-Stage Seebeck Effect in Charged Colloidal Suspensions.

We discuss the peculiarities of the Seebeck effect in stabilized electrolytes containing the colloidal particles. Its unusual feature is the two stage character, with the linear increase of differential thermopower as the function of colloidal particles concentration during the first stage (“initial state”) and dramatic drop of it at small during the second one (“steady state”). We show that the properties of the initial state are governed by the thermo-diffusion flows of the mobile ions of the stabilizing electrolyte medium itself and how the colloidal particles participate in the formation of the electric field in the bulk of the suspension. In its turn, we attribute the specifics of the steady state thermoelectric effect the massive colloidal particles undergoing slow thermal diffusion and the break down of their electro-neutrality in the vicinity of electrodes.

Influence of the multiwall carbon nanotubes on the thermal properties of the Fe–Cu nanocomposites

The relative linear expansion (ΔL/L0), coefficient of linear thermal expansion (CTE), differential scanning calorimetry (DSC), thermal conductivity and thermopower (ETP) of the Fe–Cu-MWCNT nanocomposites (Fe:Cu ratio was 4:1; MWCNT = multi-wall carbon nanotubes of 0, 0.5, 1.0 and 2.0 vol% concentration) were measured and analyzed. It was found that MWCNTs effect on thermal behaviour on these nanocomposites varies in different temperature range and the magnitude of the effect depends on the MWCNTs content. The MWCNTs effect on temperature behaviour is mainly realized via blocking the access of copper atoms to iron grains by the MWCNTs atoms. These processes as well as effect of MWCNTs on the condition of the α-Fe → γ-Fe transformation determine temperature behaviour of the nanocomposites in the range 550–700 °C. Insignificant dependence of the relative expansion and coefficient of linear thermal expansion on temperature for the nanocomposites with 2.0 vol% of the MWCNTs indicates perceptiveness of this composition for application, particularly in motor vehicle industry.

Length-dependent Seebeck effect in single-molecule junctions beyond linear response regime

In the present work, we theoretically study characteristics of the nonlinear Seebeck effect in a single-molecule junction with chain-like bridge of an arbitrary length. We have employed tight-binding models to compute the electron transmission through the system. We concentrate on the analysis of dependences of thermovoltage Vth and differential thermopower S on the bridge length. It is shown that Vth becomes stronger and S grows as the bridge lengthens. We discuss the effects of the bridge coupling to the electrodes and of specific characteristics of terminal sites on the bridge on the length-dependent Vth and S, which appear when the system operates beyond the linear response regime.

On the thermopower and thermomagnetic properties of Er x Sn1–x Se solid solutions

The ErxSn1–xSe system is characterized by a significant deviation of the temperature dependence of the differential thermopower from linearity at temperatures below room temperature and a change in the sign of the thermomagnetic coefficient. The deviation of the thermopower of ErxSn1–xSe samples in the nonequilibrium state from linearity is found to be caused mainly by the entrainment of charge carriers by phonons αph. The statistical forces of electronic entrainment, Aph(e), are estimated.

Anomalous increase of thermopower in epitaxial graphene

Thermoelectric effect in epitaxial graphene formed on the surface of a semiconductor is considered in the context of the Davydov model. The approach based on the Kubo formula for the conductivity and differential thermopower is used. It is shown that near the edges of the semiconductor bandgap, the thermopower of epitaxial graphene increases by more than four times as compared to the thermopower near the Dirac point. A possible explanation of this effect is given.

Polarization-based perturbations to thermopower and electronic conductivity in highly conductive tungsten bronze structured(Sr,Ba)Nb2O6: Relaxors vs normal ferroelectrics

Electrical conductivity, thermopower, and lattice strain were investigated in the tetragonal tungsten bronze structured $({\mathrm{Sr}}_{x},{\mathrm{Ba}}_{1\ensuremath{-}x}){\mathrm{Nb}}_{2}{\mathrm{O}}_{6\ensuremath{-}\ensuremath{\delta}}$ system for $0.7gxg0.4$ with large values of \ensuremath{\delta}. These materials show attractive thermoelectric characteristics, especially in single-crystal form. Here, the Sr/Ba ratio was changed in order to vary the material between a normal ferroelectric with long-range polarization to relaxor behavior with short-range order and dynamic polarization. The influence of this on the electrical conduction mechanisms was then investigated. The temperature dependence of both the thermopower and differential activation energy for conduction suggests that the electronic conduction is controlled by an impurity band with a mobility edge separating localized and delocalized states. Conduction is controlled via hopping at low temperatures, and as temperature rises electrons are activated above the mobility edge, resulting in a large increase in electrical conductivity. For relaxor ferroelectric-based compositions, when dynamic short-range order polarization is present in the system, trends in the differential activation energy and thermopower show deviations from this conduction mechanism. The results are consistent with the polarization acting as a source of disorder that affects the location of the mobility edge and, therefore, the activation energy for conduction.

Electrical properties of ferromagnetic Ni2MnGa and Co2CrGa Heusler alloys

The electrical properties of ferromagnetic Ni2MnGa and Co2CrGa Heusler alloys are measured in the temperature range 4–900 K. The effect of the energy gap near the Fermi level in the electronic spectrum on the behavior of electrical resistivity and absolute differential thermopower is discussed.

Effect of plastic deformation on physical properties and structure of the shape memory alloy Ti49.5Ni50.5

The effect of severe plastic deformation by torsion (SPDT) in Bridgman anvils at a high pressure (6 GPa) on the physical properties and crystal structure of the shape memory alloy Ti49.5Ni50.5 has been studied. The behavior of the thermal expansion, electrical resistivity, absolute differential thermopower, Hall coefficient, magnetic properties, and optical characteristics of the amorphous/nanocrystalline and submicrocrystalline alloys obtained by the SPDT with subsequent heat treatment at 800 K has been discussed.

Electric transport in R 2MGe 6 ternary compounds (R = La, Ce, Gd, Tb, Dy, Ho; M = Mn, Ni, Cu)

Polycrystalline samples of the intermetallic compounds La 2MnGe 6, Ce 2MnGe 6, La 2CuGe 6, Ce 2CuGe 6, and R 2NiGe 6 (R = Gd, Tb, Dy, Ho), which belong to the Ce 2CuGe 6 type of structure ( Amm2 or Cm2 m space group), were studied by means of the electrical resistivity and differential thermopower measurements. They exhibit the metallic-like behavior in the temperature range from 5 to 290 K. The peculiarities in both resistivity and thermopower temperature dependencies correlate with corresponding magnetic transition T tr temperatures.

Influence of crystallite-boundary potential barriers on the thermopower and peltier effect in polycrystalline ferroelectric semiconductors

The influence of local charged states at crystallite boundaries on the thermoelectric effects in polycrystalline ferroelectrics is considered. It is shown that the differential thermopower and the Peltier coefficient depend on the height of the crystallite-boundary potential barriers. The possible manifestation of an anomalous behavior of the thermopower in the vicinity of the Curie ferroelectric point is demonstrated.

Differential thermopower of a CNT chiral carbon nanotube

The differential thermopower of a chiral carbon nanotube (CNT) was calculatedusing a tractable analytical approach. We obtained an expression for theelectrical conductivity σ and the thermopower α. The resultswere numerically analysed. We noted from the values of α that thematerial can behave as a semimetal, n-type semiconductor and a p-typesemiconductor, depending on the parameters of the CNT. We propose the use ofthe CNT as a thermoelement.

Spin-dependent thermal and electrical transport in a spin-valve system

Within the framework of Bu{close_quotes}ttiker{close_quote}s gauge invariant and charge conservation dc transport theory, the spin-dependent thermal and electrical transport in a ferromagnet-insulator-ferromagnet tunnel junction is investigated at finite bias voltage and finite temperature. It is observed that the relative orientations of magnetizations in the two ferromagnetic (FM) electrodes as well as temperature have remarkable effects on the differential conductance, thermopower, Peltier effect, and thermal conductivity. At low temperature the quantum resonant tunneling is predominant, leading to the deviation of classical transport theory, while the transport of electrons are crucially governed by thermal processes at high temperature. The so-called spin-valve phenomenon is clearly uncovered for both the differential conductance and the thermal conductivity at low temperature. The Wiedemann-Franz law is examined, and the inelastic tunneling spectroscopy is also discussed. Our findings are expected to be measured in the near future.

V–Mn–{Sn,Sb} ternary systems

The isothermal section of the phase diagrams of ternary V–Mn–Sn and V–Mn–Sb systems has been investigated at 770 and 870 K, respectively. No ternary compounds were observed. The systems are characterised by the existence of solid solutions based on the binary compounds. The temperature dependence of the electrical resistivity and differential thermopower for (V,Mn) 3Sb solid solution has been measured.

Isothermal section of the Ti–Mn–Sn system and crystal structure of the TiMnSn 4 compound

The isothermal section of the phase diagram of ternary Ti–Mn–Sn system has been investigated at 770 K. The existence of new TiMnSn 4 ternary compound was established and its crystal structure was determined. TiMnSn 4 stannide crystallizes in the Mg 2Ni structure type (space group P6 222 , a=0.55537(1) nm, c=1.40326(2) nm). For the given compound the temperature dependences of electrical resistivity, differential thermopower and magnetic susceptibility were investigated. On the basis of binary Mn 3Sn, Ti 6Sn 5 and Ti 3Sn compounds the solid solutions were formed.

Magnetic and electrical properties of R 2CuGe 6 compounds (R=Y, Ce, Nd, Gd, Tb, Dy, Ho, Er, Yb)

The temperature dependence of the magnetic susceptibility of the R 2CuGe 6 (R=Y, Gd, Tb, Dy, Ho, Er, Yb) compounds was measured in the range 84–300 K. It is shown that these rare earth compounds are Langevin type paramagnets except the Y 2CuGe 6 compound which is a Pauli paramagnet with low and temperature independent magnetic susceptibility. The resistivity of the compounds with R=Y, Ce, Nd, Gd, Tb, Ho, Yb was measured in the range 78–380 K. The differential thermopower of the Ce 2CuGe 6 and Tb 2CuGe 6 compounds was investigated in the range 78–380 K. Specific resistivity of the above-mentioned germanides increases linearly with increasing temperature and adopts values normally found in intermetallics.

The Modulation of Thermoelectric Power by Chemisorption A New Detection Principle for Microchip Chemical Sensors

The differential thermopower (Seebeck effect) depends on the properties of two materials that form a junction. If one of the two materials is chemically sensitive, a thermocouple can constitute a chemical sensor that provides a chemically dependent signal similar to that of a chemically sensitive field‐effect transistor (CHEMFET). Thermocouples were fabricated from junctions of thin films of indium oxide and gold (Au) sputtered onto a glass substrate. The device, with the junctions and , was heated such that the two junctions were kept at slightly different temperatures. Thus, a thermoelectric voltage (Seebeck effect) was generated at the junctions. When the device was exposed to a continuous flow of pure air or synthetic air with traces of nitric oxide , the Seebeck voltage was found to be extremely sensitive to the contamination in the air, as expected from theory. We demonstrate the operation of a new chemical sensor that works due to the modulation of the Fermi energy as a result of chemisorption. © 2000 The Electrochemical Society. All rights reserved.

The ternary Er–Co–Sn system

Abstract The isothermal section of the phase diagram of the Er–Co–Sn ternary system has been constructed at 670 K. The existence of seven ternary intermetallic compounds which crystallize with known structure types has been confirmed. The temperature dependence of the magnetic susceptibility (χ) for ErCo3Sn and Er3Co6Sn5 has been measured. The ErCo3Sn stannide orders ferrimagnetically at 24 K, and the Er3Co6Sn5 stannide is a Curie–Weiss paramagnet. For Er3Co6Sn5, electrical resistivity (ρ) and differential thermopower (α) have been measured in the range 80–400 K.

Differential thermopower of a superlattice in a strong electric field

The effect of an electric field on the differential thermopower α(E) of a one-dimensional superlattice is investigated in the semiclassical approximation. A nonmonotonic temperature dependence of α(0) is established for a degenerate electron gas. It is shown that, in principle, an electric field can be used to control the thermoelectric properties of superlattices.

Phase dependent differential thermopower ofs-wave-superconductor–normal-metal–d-wave-superconductor junctions: Pair-breaking effects and Gaussian fluctuations

We start with revisiting our previous results on thermoelectric response of s-wave-superconductor--normal-metal--$s$-wave-superconductor $(\mathrm{SNS})$ configuration in a C-shaped ${\mathrm{Bi}}_{x}{\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{y}$ sample in order to include strong fluctuation effects. Then, by appropriate generalization of the Ginzburg-Landau theory based on admixture of s-wave $(S)$ and d-wave $(D)$ superconductors, we consider a differential thermoelectric power (TEP) of s-wave-superconductor--normal-metal--$d$-wave-superconductor $(\mathrm{SND})$ junction. In addition to its strong dependence on the relative phase $\ensuremath{\theta}={\ensuremath{\varphi}}_{s}\ensuremath{-}{\ensuremath{\varphi}}_{d}$ between the two superconductors, two major effects are shown to influence the behavior of the predicted TEP. One, based on the chemical imbalance at $\mathrm{SD}$ interface, results in a pronounced maximum of the TEP peak near $\ensuremath{\theta}=\ensuremath{\pi}/2$ (where the so-called $s+id$ mixed pairing state is formed) for two identical superconductors with ${T}_{\mathrm{cd}}{=T}_{\mathrm{cs}}\ensuremath{\equiv}{T}_{c}.$ Another effect, which should manifest itself at $\mathrm{SD}$ interface comprising an s-wave low-${T}_{c}$ superconductor and a d-wave high-${T}_{c}$ superconductor with ${T}_{\mathrm{cd}}\ensuremath{\ne}{T}_{\mathrm{cs}},$ predicts ${S}_{p}\ensuremath{\propto}{T}_{\mathrm{cd}}\ensuremath{-}{T}_{\mathrm{cs}}$ for the TEP peak value. The experimental conditions under which the predicted behavior of the induced differential TEP can be measured are discussed.