Thermoelectric Power Changes Research Articles

Thermoelectric power of MgB 2

Thermoelectric power (TEP) of MgB 2 and its changes with the superconducting transition temperature ( T c) have been investigated. MgB 2 samples synthesized with different techniques––sample 1 by the encapsulation method and sample 2 by the high pressure and high temperature technique––showed different T c ( T c of sample 1= 38.7 K, and T c of sample 2 = 40.4 K). The characteristic features of the TEP of these samples––low temperature linear behavior, deviation from the low temperature linear behavior at a certain temperature, and an almost saturating value at ∼300 K––were found to vary systematically with T c, consistent with the previously reported TEP changes in Mg 1− x Al x B 2. These changes of the TEP behaviors with T c in the superconducting diborides system are discussed in comparison with those of high T c cuprates and bismuthates. The common feature of the saturating TEP at high temperatures suggests the importance of an anharmonic electron–phonon interaction.

1143. Fe-Cr2元合金およびFe-Cr-Ni3元合金の熱起電力とXPS分析による価電子領域の電子状態の関係

In order to clarify the mechanism behind the change in thermoelectric power (TEP) of Fe-Cr binary alloys and Fe-Cr-Ni ternary alloys due to Cr concentration, using these alloys with various Cr concentrations, dependence of TEP on Cr concentration was investigated. According to the Mott-Jones theory, TEP is largely related to electron density of states at the Fermi level. The electron density of states for the alloys in valence band was measured with X-ray photoelectron spectroscopy (XPS), and theoretically calculated TEP from the XPS spectrum was compared with experimentally measured TEP. Electron density of states in valence band of the both alloys changed due to Cr concentration, and the theoretically calculated TEP from XPS spectrum and the experimentally measured TEP similarly changed with Cr concentration. We think that the change in TEP with Cr concentration is due to the change in electron density of states with Cr concentration.

Mechanism of the change in thermoelectric power of cast duplex stainless steel due to thermal aging

It has been shown that thermoelectric power (TEP) measurement is an effective method for evaluating thermal aging of cast duplex stainless steel. However the mechanism underlying the relationship between thermal aging and TEP has not yet been thoroughly explained. In this study, the relationship between TEP and the microstructural changes caused by thermal aging was investigated to help clarify the mechanism. It is well known that phase separation in the ferrite phase proceeds gradually due to thermal aging and that Cr-rich phases are created in the ferrite phase. Therefore, close attention was paid to the effect of Cr concentration on the TEP. Fe–Cr–Ni alloys with different Cr concentrations in the range from 5 to 75% were prepared and the TEP measured for each. As a result, the TEP decreased with a Cr concentration between 5 and 65% but increased at 65% or higher. The Cr concentration distribution in ferrite phases of thermal aged cast duplex stainless steel was measured and its data were combined with the TEP values of the alloys. We tried to predict changes in the TEP of cast duplex stainless steel due to thermal aging, and eventually confirmed the tendency that the composed TEP increased with thermal aging. Considering the fact that TEP is largely related to the electron density of states at the Fermi level, we measured the electron density of states by means of XPS (X-ray photoelectron spectroscopy), and found that changes in the structure of the spectrum due to thermal aging had the same tendency as the experimentally measured TEP. Consequently, we noted the mechanism that the TEP of cast duplex stainless steel increased with thermal aging and confirmed the effect of the electron density of states on TEP.

鋳造2相ステンレス鋼の熱時効に伴うフェライト相のCr濃度変調による熱起電力の変化

Cast duplex stainless steel is frequently used in main coolant pipes of PWR (Pressurized water reactor) type nuclear power plants because of its excellent material strength, toughness and superior corrosion resistance. However, it is known that Cr concentration fluctuation in ferrite phase occurs due to thermal aging when this material is exposed to temperature over 300°C. As a result, the toughness decreases. In previous studies, it has been shown that thermoelectric power (TEP) is an effective parameter in non-destructive evaluation for thermal aging of cast duplex stainless steel. In this study, mechanisms of increase in TEP due to Cr concentration fluctuation caused by thermal aging were investigated. Referring to Cr concentration fluctuation in ferrite phase of thermal aged cast duplex stainless steel measured by 3D-atom prove, Fe-Cr-Ni alloys with different Cr concentrations, which represented local area Cr fluctuated, were prepared. Then, TEP, electrical conductivity and thermal conductivity of the alloys were measured, and the relationships between these values and Cr concentration were determined. Using the relationships and the Cr concentration fluctuations, TEP of thermal aged cast duplex steel were composed in the case when each Cr-fluctuated area acted in series connection and in parallel connection. Then, the changes in TEP due to thermal aging were simulated, and compared with that in experimentally measured TEP. As a result, recurrence curves of Cr concentration to TEP, electrical conductivity and thermal conductivity were downward convex parabolas. Therefore, it was found that, by means of creation of high and low Cr area in ferrite phase due to thermal aging, TEP, electrical conductivity and thermal conductivity of the whole material increased. When each Cr fluctuated area acted in parallel connections, increase in TEP due to thermal aging became larger and the change in the composed TEP came close to that in the experimentally measured TEP.

Density of localized states in (Pb0.78Sn0.22)0.95In0.05Te solid solutions

The hopping conductivity and the Seebeck coefficient have been measured in Pb0.78Sn0.22Te with 5 at. % In and supplementary donor doping with Cl. The experimental data obtained are compared with similar results for supplementary acceptor doping with Tl. At temperatures of 150 K and higher, the thermoelectric power changes its sign from positive to negative on the introduction in sufficient amounts of either donors or acceptors. An analysis of the dependence of the thermoelectric power on the content of supplementary donors and acceptors yields the density of localized indium states as a function of energy. The function is essentially nonmonotonic, exhibiting both a density-of-states peak and a minimum between this peak and the conduction band.

Thermoelectric powerand band spectrum transformation in Y1-xCaxBa2-xLaxCu3Oy

The superconducting and normal-state transportproperties (resistivity ρ and thermoelectric power S) oftwo sets of ceramic samples with compositionY1-xCaxBa2-xLaxCu3Oy (x = 0-0.4) have been investigated.The co-doping effect was studied at different conditions of the oxygen subsystem, namely, at anear-stoichiometric oxygen content and at that decreased by annealing in vacuum atmosphere.The thermoelectric power changes only slightly with increasing doping level,while the S(T) dependence acquires additional features,exhibiting a linear increase with decreasing temperature forheavily-doped samples and a rise in the S(T) curve slope as x grows.The results obtained are analysed in terms of aphenomenological narrow-band model that makes it possible to determinethe band spectrum parameters in the normal state and to tracetheir changes with varying composition.In co-doped Y1-xCaxBa2-xLaxCu3Oy, impuritieswith valencies different from those of the native cations cancel out the influence of one another on thecharge balance in the lattice.All the results obtained indicate that the normal-state and superconducting properties of theinvestigated system are mainly determined by this compensation effect.Comparison of the variation of the critical temperatureTc with the changing conduction bandwidth WD shows thatthere is a correlation between these parameters, according towhich the superconducting properties of doped YBa2Cu3Oydepend strongly on the parameters of the band spectrum structurein the normal state.Analysis of how the conduction band is modified and S(T) transforms suggests that calcium isresponsible for additional states in the conduction band.

Magnetoresistance and thermoelectric power of Sr 1− xK xBiO 3: a second family of BiO-based superconductors

We have measured the temperature dependence of magnetoresistance and thermoelectric power (TEP) for the Sr 1− x K x BiO 3 superconductor ( x= 0.45 – 0.6). The onset temperature of superconductivity in resistivity measurements is 12.5 K and the resistivity goes to zero at 10.2 K. The upper critical field ( H c2 (0)) and the coherence length (ζ(0)) determined by the criterion ρ( H = H c2 ) 0.9ρ n , where ρ n is the normal state resistivity, are estimated to be 5.09 Tesla and 79.1Å, respectively. TEP at room temperature has a small negative value ( S = −1.96 μV/K) and its temperature dependence shows to distinct features. The sign of TEP changes from negative to positive at 210 K. As lowering the temperature, the negative slope of TEP (d S/dT) decreases and becomes rather flat at around 160 K, which is a feature noted in other BiO-based superconductors.

Correlation between the microstructural evolution of a 6061 aluminium alloy and the evolution of its thermoelectric power

The thermoelectric power (TEP) of a 6061 Al alloy was measured during isothermal ageing performed between 200 and 500°C. A correlation between the change in TEP and the precipitation kinetics of various metastable phases was established using TEM and HRTEM observations and resistivity measurements. It was demonstrated that the TEP kinetics allow an assessment of the residual concentration of solute in the final equilibrium state. Furthermore, it was shown that the non-monotonous TEP changes reflect the microstructural transformations occurring in the alloy. In particular, the transition between two phases can be detected, owing to the change of the intrinsic effect or of the chemical composition of the precipitates.

Hall effect and thermoelectric power in CeCu 5.9Au 0.1 and CeCu 6

We have investigated the Hall coefficient ( R H) and thermoelectric power (TEP) on single crystals of CeCu 5.9Au 0.1, which shows non-Fermi liquid anomaly, and on CeCu 6 as a reference. TEP exhibits a large positive peak at ∼40 K, below which it becomes highly anisotropic. Au substitution causes no drastic change in TEP. The anisotropy in R H( T) is small above 10 K, and it showed a large dependence on the field direction in both compounds below 10 K. Most interesting aspect of the present results is the large anisotropy in the Au substitution effect on R H( T), which might correlate with the anisotropy in the spin fluctuation.

Spin fluctuations and properties of the thermoelectric power of nearly ferromagnetic iron monosilicide

The thermoelectric power of nearly ferromagnetic iron monosilicide, which passes through an electronic semiconductor-metal transition with increasing temperature, is investigated theoretically. The results of this investigation indicate that a sizable paramagnon-related increase in charge carriers can occur in nearly ferromagnetic semiconductors, and that spin fluctuations can modify the electronic spectrum and thereby renormalize the diffusion component of the thermoelectric power. The transition from semiconductor to metal decreases the paramagnon component sharply and the thermoelectric power changes sign, which agrees with experimental data for iron monosilicide.

Spin-gap like behavior observed in intermediately doped polyacetylene

A notable decrease in ESR spin susceptibility was found near 130 K in intermediately ClO 4 − -doped v -(CH) x . The absence of the corresponding change in thermoelectric power suggests that it is associated with a spin-charge separation. The possible origin is discussed with respect to the structural change in (CH) x .

Electrical conduction behaviour in -type below room temperature

Electrical transport in polycrystalline ceramics of K-type has been investigated as a function of temperature using complex-plane impedance analyses, dielectric properties, DC conductivities by the four-probe method, thermoelectric power and magnetic susceptibilities. The bulk conductivities were obtained using the complex-plane impedance analyses. The magnetic properties indicate that antiferromagnetically ordered magnetic moments are canted and there is a weak ferromagnetic contribution below the Néel temperature of 113 K. The thermoelectric power changes from positive values to negative ones at around 200 K with increasing temperature. Above about 200 K, the dielectric relaxation peak due to a hopping process involving small polarons manifests itself. The temperature dependencies of the dielectric relaxation process and the bulk conductivities suggest that the charge carriers responsible for the conduction are strongly localized. This is directly supported by the fact that the activation energy for the bulk conduction is nearly equal to that for the dielectric relaxation. The experimental results above about 200 K have been interpreted in terms of a hopping process involving small polarons. At lower temperatures, either multiphonon jumping processes of small polarons are frozen out or charge transport between impurity states takes place.

Thermodynamic properties of the molten Tl‐GeTe4 system

AbstractFrom the electromotive force method, the chemical potential or activity of Tl in the molten Tl‐GeTe4 system has been measured as a function of composition and temperature. The chemical potential of Tl has then been separated in terms of partial entropy and enthalpy, the both quantities showing an abrupt change from negative to positive values around the stoichiometric composition corresponding to Tl8GeTe4. The integral molar entropy and enthalpy, ΔSm and ΔHm, show sharp minima at the composition Tl8GeTe4 where the electrical conductivity has a sharp minimum and the thermoelectric power changes its sign. From these results it is suggested that the strong interaction between Tl and Te leads to form a chemical entity Tl2Te and the observed thermodynamic properties can be interpreted as a mixture of Tl2Te and unbounded atomic Ge and Te in the GeTe4‐rich side and or atomic Ge and Tl in the Tl‐rich side.

Electrical and Thermoelectric Properties of CuInTe2in the Solid and Liquid Phases

Abstract Measurements of the electrical conductivity and thermoelectric power of CuInTe2 in the temperature range from 400°C to 970°C shows that the thermoelectric power changes sign from positive in the solid state to negative in the liquid state above its melting point. The experimental data were explained on the basis of a model developed for the density of states and electrical transport in solid amorphous semiconductors [1]. The activation energy from electrical conductivity was found to be 0.31 ev for the solid and 0.79 ev for the liquid and the coefficient of the linear decrease of the energy gap with temperature was found to be 1.18 × 10−4 ev/°K.

Thermoelectric voltage study of 1T-TaS2 using temperature dependent scanning tunneling spectroscopy

Using an ultra high vacuum (UHV) scanning tunneling microscope where the sample is cooled while the tip remains close to room temperature, we measured the thermoelectric voltage induced by the large thermal gradient between the tip and sample. Using tunneling thermometry technique we studied the change of electronic structures of 1T-TaS2 from room temperature to 40 K. At the temperature for the nearly commensurate to commensurate transition, we found an abrupt change of the thermoelectric power from a very small value to about 0.15 mV/K.

Thermoelectric power characterization of a 2024 aluminum alloy during solution treatment and aging

The solution treatment and aging of a 2024 aluminum alloy was studied using the thermoelectric power (TEP) measurement technique, and the results compared to those obtained by microhardness and optical microscopy. The TEP value changes with solution treatment temperature and duration and reaches a maximum value for solution treatment at 500 °C. The changes in TEP during solution treatment are caused by changes in the solubility of the alloying elements in α-Al. In the artificial aging process, the TEP value decreases with increasing aging time, but exhibits different characteristics for different stages of aging. In the initial stage, the TEP value decreases slowly and shows a fluctuating behavior for aging in temperatures below 190 °C. This fluctuation is caused by G.P. zone, G.P.B. zone, θ″, θ′, S″, and S′ formation which make different contributions to the TEP value. The TEP values corresponding to maximum microhardness for different aging temperatures are the same for a given solution treatment temperature. After the peak age, the TEP values decrease very quickly because the solubility of the alloying elements in α-Al decreases with aging time. The micro structural changes caused by precipitation during aging which cannot be observed by the light optical microscope were successfully monitored by the TEP measurement technique.

Nonstoichiometry and electrical conduction of CuO

Abstract Electrical conductivity, thermoelectric power and weight changes were measured between room temperature and 800 or 1000 °C on CuO with varying sintering temperatures to determine nonstoichiometric and defect properties of CuO. CuO was confirmed to be a metal deficient p-type semiconductor with copper vacancies at low temperature. Copper vacancy formation was favored with decreasing sintering temperature indicating the negative enthalpy of the defect generation reaction. Nonstoichiometry in Cu 1−y O was a few percent at 700–900 °C. Conduction in Cu 1−y O was judged to be due to hopping of charge carriers with an activation energy of 0.1 eV. The band gap energy of CuO, estimated from high temperature intrinsic conductivity was ~ 1.2 eV.

Electronic and Structural Properties of the Liquid (Tl1/2Pb1/2)‐Se System

AbstractThe electrical conductivity, magnetic susceptibility, and thermoelectric power in the liquid (Tl1/2Pb1/2) Se system are measured over wide temperature and composition ranges. It is observed that the electrical conductivity in the system sharply falls near the stoichiometric composition of Tl2Pb2Se3 and the magnetic susceptibility has a diamagnetic maximum at this composition, where the thermoelectric power changes its sign. In addition, the DTA investigation shows that the liquidus temperature of the system has a maximum around this composition. These results suggest that a short‐range order appears around the composition of Tl2Pb2Se3 in the liquid (Tl1/2Pb1/2)‐Se system. The delocalized electron analysis using both susceptibility and conductivity data suggests that the bonding nature of liquid Ti2Pb2Se3 is rather ionic. The radial distribution study by neutron diffraction also exhibits that the first peak position of g(r) for liquid Tl2Pb2Se3 is located near the ionic bond distance of metal and chalcogen atoms. On the other hand, covalent Se‐ Se bonds are formed in the Se‐rich composition range.

Dielectric and thermoelectric studies on TiO2based materials

Abstract Thermoelectric power (S) and permittivity measurements were studied for TiO2 and Fe3+ loaded TiO2. The changes in thermoelectric power as a function of temperature and that of the dispersion of dielectrics has been attributed to the interaction of Fe3+ with TiO2 in the matrix. When such an Interaction is not present there is no appreciable change in the thermoelectric power and dielectric dispersion.

Effect of impurities on thermoelectric power in thallium blue bronze Tl 0.3MoO 3

Temperature dependence of thermoelectric power of thallium blue bronze Tl 0.3MoO 3 doped with K and W atoms impurities are presented. The experimental results display that thermoelectric power data for all the doped samples can be fitted to an expression of the type, S = At + B/ T, below and above T p . With the addition of impurities, the absolute values of the thermoelectric power decrease and the temperature of the sign change of thermoelectric power T s increases. The mechanisms of drift diffusion and phonon drag of the thermoelectric power are involved. The donor effect of the impurities and the influence of weak inter-chain coupling are proposed.