Thermoelectric Power Coefficient Research Articles

A modified Green-Naghdi fractional order model for analyzing thermoelectric MHD

PurposeWhereas, the classical Green-Naghdi Type II (GN-II) model struggles to accurately represent the thermo-mechanical behavior of thermoelectric MHD due to its inability to account for the memory effect. A new mathematical model of the GN-II theory incorporates a fractional order of heat transport to address this issue.Design/methodology/approachThe employment of the matrix exponential method, which forms the basis of the state-space approach in contemporary theory, is central to this strategy. The resulting formulation, together with the Laplace transform techniques, is applied to a variety of problems. Solutions to a thermal shock problem and to a problem of a layer media both without heat sources are obtained. Also, a problem with the distribution of heat sources is considered. The numerical technique is used to achieve the Laplace transform inversion.FindingsAccording to the numerical results and its graphs, the influences of the fractional order parameters, figure-of-merit factor, thermoelectric power and Peltier coefficient on the behavior of the field quantities are investigated in the new theory.Originality/valueThe new modeling of thermoelectric MHD has advanced significantly as a result of this work, providing a more thorough and precise tool for forecasting the behavior of these materials under a range of thermal and magnetic conditions.

Character of the interaction in the As2Te3-TISe System and Electrophysical Propertes of the Phases Obtained

The character of the interaction in the As2Te3-TlSe system was studied by the methods of Differential Thermal Analysis (DTA), X-ray Diffraction (XRD), Microstructure analysis (MCA), and also by measuring the microhardness and determining the density of alloys, and state diagram was constructed. It is established that the As2Te3-TlSe state diagram is a quasibinary section of the triple mutual system As, Tl // Se, Te. Two new compounds, TlAs2Te3Se and Tl3As2Se3Te3, are formed in the As2Te3-TlSe system. Both compounds are obtained in the vitreous state. Solid solutions based on As2Te3 at room temperature reach up to 3 mol.% TlSe, and based on TlSe-2 mol.% As2Te3. The electrical conductivity and thermoelectric power coefficient of the (As2Te3)1-x (TlSe)x solid solutions have been measured as functions of temperature.

Seebeck coefficient of Cr100−zOsz alloy system

The magnetic phase diagram of the Cr100−zOsz alloy system exhibits possible quantum critical behavior (QCB), with commensurate spin-density-wave to paramagnetic (CSDW-PM) phase line terminating at z ≈ 14, in a superconducting dome at z ≈ 12. Also indicated is the co-existence of SDW antiferromagnetism (AFM) and superconductivity (SC) for the z = 12.2 sample with a bcc structure. Considering the unique behaviour in the Cr100−zOsz system, this study reports on an investigation into the temperature dependence of the thermoelectric power or Seebeck coefficient, ST. With S(T) sensitive to the electronic structure and scattering mechanisms it is used here in order to investigate the unique magnetic behaviour observed in this alloy. ST measurements were performed on polycrystalline Cr100−zOsz (2.1 ≤ z ≤ 14.1) samples, as confirmed by XRD to be in a single bcc phase. The low-temperature S(T) behaviour is expressed in the form S = aT + bT3, where a and b are constants that were determined to discuss the possible contributions of phonon and/or magnon drag to S. Resulting a(z) and b(z) behaviour indicate anomalies that can be associated with three crucial points in the Cr100−zOsz magnetic phase diagram: (i) at z ≈ 8 is associated with the destabilization of the CSDW phase with the continual addition of Os into the system, (ii) at z ≈ 12 where the SC properties manifest and (iii) at z ≈ 13 associated with quantum critical behaviour this the system. Considering dS/dT where T approaches 0 K, as function of z, clear anomalies are observed at z ≈ 12 and 13, which, are associated with the onset of SC and QCB in this system. The present results suggest that S is a decisive experimental parameter in characterizing anomalous behaviour reflected in the magnetic phase diagram of Cr100−zOsz.

Low thermal conductivity and interface thermal conductance in SnS2

After the discovery of graphene, there have been tremendous efforts in exploring various layered two-dimensional (2D) materials for their potential applications in electronics, optoelectronics, as well as energy conversion and storage. One of such 2D materials, SnS2, which is earth abundant, low in toxicity, and cost effective, has been reported to show a high on/off current ratio, fast photodetection, and high optical absorption, thus making this material promising for device applications. Further, a few recent theoretical reports predict high electrical conductivity and Seebeck coefficient in its bulk counterparts. However, the thermal properties of SnS2 have not yet been properly explored, which are important to materialize many of its potential applications. Here, we report the thermal properties of SnS2 measured using the optothermal method and supported by density functional theory (DFT) calculations. Our experiments suggest very low in-plane lattice thermal conductivity (\k{appa} = 3.20 +- 0.57 W m-1 K-1) and cross-plane interfacial thermal conductance per unit area (g = 0.53 +- 0.09 MW m-2 K-1) for monolayer SnS2 supported on a SiO2/Si substrate. The thermal properties show a dependence on the thickness of the SnS2 flake. Based on the findings of our DFT calculations, the very low value of the lattice thermal conductivity can be attributed to low group velocity, a shorter lifetime of the phonons, and strong anharmonicity in the crystal. Materials with low thermal conductivity are important for thermoelectric applications as the thermoelectric power coefficient goes inversely with the thermal conductivity.

Impact of nanorod morphology on microstructure, magnetic and electrical properties of NixCo1-xFe2O4

A series of NixCo1-xFe2O4 (x = 0, 0.25, 0.5, 0.75 and 1) was successfully synthesized via hydrothermal method. From XRD analysis, the pure phase formation of Ni–CoFe2O4 (NCFO) was confirmed and the crystallite size ranged from 33 to 44 nm. Besides, the variation of theoretical lattice parameter with x-content was in a good agreement with experimental ones. Field Emission Scanning Electron Microscope (FESEM) revealed the formation of nanorod shapes with gradual decrease in length and diameter with addition of Ni2+ ions. Energy Dispersive X-ray analysis (EDX) confirmed the purity of prepared samples. Magnetic parameters (Ms, Mr and Hc) showed a gradual decrease with addition of Ni2+ ions. Meanwhile, both Coercivity and Curie temperature were enhanced in our studied nanorod compositions compared to their corresponding nanosphere compositions. Variation of DC resistivity and thermoelectric power coefficient were studied in the temperature range 385–548 K. The sign of the thermoelectric power coefficient could determine the type of charge carriers. Moreover, the conduction mechanism was deduced from activation energy values. Finally, the cation distribution was proposed such that it could verify the variation of lattice parameter and magnetization of each composition as well as the behavior of resistivity and thermoelectric power.

Correlation of cation distribution with structure, magnetic and electrical properties of ultrafine Ni2+-doped CoFe2O4

This work presents the estimation of cation distribution of ultrafine NixCo1−xFe2O4 nano-ferrites (x = 0, 0.25, 0.5, 0.75 and 1) from structure, magnetic and electrical investigations. “Sol gel” was the method used to synthesize Ni–Co ferrites. Ni2+-doped CoFe2O4 nanostructure has a broad range of electromagnetic applications due to its controllable magnetic and electrical properties. From XRD patterns, the formation of pure phase was obvious, and the crystallite size ranged from 9 to 12 nm. These sizes are small enough to achieve suitable signal-to-noise ratio for high-density recording media and have more opportunities for technological application, especially in medical fields. Besides, the variation of theoretical lattice parameter with x-content was in a good agreement with experimental ones. Field Emission Scanning Electron Microscope (FESEM) revealed the formation of small nanosphere particles with gradual size reduction on addition of Ni2+ ions. Energy-Dispersive X-ray analysis (EDX) confirmed the purity of prepared samples. Magnetic parameters (Ms, Mr and Hc) were determined from Vibrating Sample Magnetometer (VSM). It was found that both Ms and Hc have gradual decrease with increasing x-content. Curie temperature was determined from the variation of relative permeability with temperature and showed also a gradual decrease with addition of Ni2+ ions. Temperature dependence of both DC electrical resistivity and thermoelectric power coefficient were carried out in the temperature range 385–548 K. The resistivity showed a gradual decrease with increasing x-content. However, the negativity of thermoelectric power coefficient showed a gradual increase with addition of Ni2+ ions. Conduction mechanism was deduced for all studied samples from activation energy values. The cation distribution was proposed such that it could verify the lattice parameter and magnetization of each composition as well as the behavior of resistivity and thermoelectric power.

Thermoelectric Power and Dielectric Studies of Cobalt-Substituted Manganese-Zinc Nanoferrites

Cobalt-manganese-zinc nanoferrites with the formula CoxMn0.5−xZn0.5Fe2O4 (x = 0.0, 0.1, 0.3, and 0.5) were prepared by chemical co-precipitation method. The formation of cubic spinel structure particles in nanometer size with no minor phase was confirmed from the XRD patterns of all the samples. The estimated average crystallite size using Scherrer’s formula was found to be in the range of 11–42 nm, in good agreement with TEM result. The measurements of thermoelectric power or Seebeck coefficient were carried out from 100 to 300 °C by the differential method. The results showed a negative value for Seebeck coefficient of samples with x = 0 and 0.1 within the whole measured interval of temperatures. It indicates the n-type semiconductor behavior. However, for the samples with x = 0.3 and 0.5, the sign of Seebeck coefficient is reversed to positive at temperatures 283 and 272 °C, respectively. Also, all the samples were found to exhibit the maximum absolute thermopower value at a certain temperature near to the sample’s Curie temperature. The dielectric properties of samples were studied in the frequency range from 500 Hz to 10 MHz at room temperature. It was found that the dielectric constant (e´) and dielectric loss (tanδ) are influenced by electron hopping mechanism between Fe2+ and Fe3+ ions. The presence of resonance peak in the tanδ curves vs frequency confirms the existence of single relaxation phenomena in the given frequency range for all the samples.

Surface morphology and electrical transport properties of Aberchrome 670 ( (E-3(admantan-2-ylidene) -4-[1-(2,5-dimethyl-3-furyl) ethyldene] dihydro-2,5-furandione)) nano thickness films

In this paper, surface morphology and electrical properties of Aberchrome 670 , [(E-3(admantan-2-ylidene)-4-[1-(2,5-dimethyl-3-furyl) ethyldene] dihydro -2,5-furandione)], thin films with nano thickness, have been studied, for the first time, to provide one with knowledge concerning microscopic features, for electrical applications of organic photochromic compounds. The atomic force microscope (AFM) has been used to convene a general spectacle about the surface. The cyclic-voltammetric measurement has been inserted to determine the electrochemical gap. The thermal effect on the electrical resistivity, the thermoelectric power and Seebeck coefficient have been measured from 298 to 373 K. The influence of the frequency on some dielectric characteristics; such as the capacitance, the temperature capacitance coefficient (T.C.C), the real part of the complex dielectric permittivity (), the dissipation factor (tan (δ)) has been studied in the frequency zone (50 -5 MHz) and temperature range (∼298–373 K) at different steady temperatures.

Small Fermi surfaces and strong correlation effects in Dirac materials with holography

Recent discovery of transport anomaly in graphene demonstrated that a system known to be weakly interacting may become strongly correlated if system parameter (s) can be tuned such that fermi surface is sufficiently small. We study the strong correlation effects in the transport coefficients of Dirac materials doped with magnetic impurity under the magnetic field using holographic method. The experimental data of magneto-conductivity are well fit by our theory, however, not much data are available for other transports of Dirac material in such regime. Therefore, our results on heat transport, thermo-electric power and Nernst coefficients are left as predictions of holographic theory for generic Dirac materials in the vicinity of charge neutral point with possible surface gap. We give detailed look over each magneto-transport observable and 3Dplots to guide future experiments.

Thermoelectric power of (Cu0.5Tl0.5)-1223 superconducting phase added with BaSnO3 nanoparticles

In this study, we report the thermoelectric power (TEP) measurements of Cu0.5Tl0.5Ba2Ca2Cu3O10-δ added with BaSnO3 nanoparticles. BaSnO3 nanoparticles were prepared by chemical co-precipitation method, while (BaSnO3)x/(CuT1)-1223 superconducting samples with 0.00 ≤ x ≤ 1.50 wt% were prepared using the solid-state reaction method. The standard four-probe technique was applied to measure DC electrical resistivity in the temperature range from 300 to 77 K. Superconducting transition temperature (Tc) increases up to 117.5 for x = 0.25 wt.% and then it decreases with further x addition. The TEP coefficient was measured as a function of temperature in a wide temperature range from ∼77 K (liquid nitrogen temperature) up to 280 K using a standard differential technique. The behavior of the obtained TEP coefficient is suit with high-Tc copper-oxide superconductors. The results were investigated according to two-band model with an extra linear term. Several parameters such as the pseudo-gap temperature (T*), Fermi energy (EF) and Fermi temperature (TF) values were calculated and discussed in terms of nanoparticles BaSnO3 addition.

Pressure effect and superconductivity in theβ−Bi4I4topological insulator

We report a detailed study of the transport coefficients of $\beta$-Bi$_4$I$_4$ quasi-one dimensional topological insulator. Electrical resistivity, thermoelectric power, thermal conductivity and Hall coefficient measurements are consistent with the possible appearance of a charge density wave order at low temperatures. Both electrons and holes contribute to the conduction in $\beta$-Bi$_4$I$_4$ and the dominant type of charge carrier changes with temperature as a consequence of temperature-dependent carrier densities and mobilities. Measurements of resistivity and Seebeck coefficient under hydrostatic pressure up to 2 GPa show a shift of the charge density wave order to higher temperatures suggesting a strongly one-dimensional character at ambient pressure. Surprisingly, superconductivity is induced in $\beta$-Bi$_4$I$_4$ above 10 GPa with of 4.0 K which is slightly decreasing upon increasing the pressure up to 20 GPa. Chemical characterisation of the pressure-treated samples shows amorphization of $\beta$-Bi$_4$I$_4$ under pressure and rules out decomposition into Bi and BiI$_3$ at room-temperature conditions.

The electrical properties of Cu2Se + Cu2O composites

The concentration and temperature dependences of the electrical conductivity and thermoelectric power of Cu2Se + Cu2O composites are investigated experimentally. It is found that a minimum at ~150°C is present in the temperature dependences of the coefficient of specific electrical resistance and thermoelectric power of the investigated samples.

Magnetic and transport properties of Gd1−xCaxCrO3 (x=0.0–0.3): Effect of orbital degeneracy in thermoelectric power

Detailed magnetic and transport properties of orthorhombic perovskites ceramics Gd1−xCaxCrO3 (x=0.0–0.3) have been reported. Magnetization measurements under both field cooled cooling (FCC) and field cooled heating (FCH) protocol reveal magnetization reversal at low temperature and low magnetic field. This indicates clear evidence of two magnetic sublattices aligned opposite to each other. The effect of Gd3+ ion on the low temperature magnetization decreases largely above x=0.2. The nature of temperature dependent dc magnetic susceptibility (χ) was Curie–Weiss like above the transition temperature (Tmax) with an effective magnetic moment (μeff) that decreased with the increase of Ca concentration. These orthochromites exhibit a temperature independent, large and positive thermoelectric power or Seebeck coefficient (S) value above 200K. Upon Ca2+ substitution, a concomitant decrease of the S value is found. The evolution of S as a function of hole concentration (Cr4+) can be well fitted by the modified Heikes formula taking into account the orbital degeneracy related to Cr3+ and Cr4+.

Influence of material parameters on reliability indicators of two-stage thermoelectric devices

It was taken a comparative analysis of the main parameters and reliability indicators of two-stage thermoelectric devices while using various combinations of the source materials, which differ by of thermoelectric power and electrical conductivity coefficients, for temperature changes from 60 K to 90 K and modes of operation from the maximum cooling capacity to the lowest failure rate. The possibility of reducing the total failure rate and increase the probability of failure of two-stage thermal power devices using of source materials with high electrical conductivity is presented. It was received a number of patterns which allows to determine the main parameters and reliability indices for different combinations of source materials compared with traditional modes of operation and temperature changes. Variants of combinations of averaged parameters of raw materials for the construction of two-stage thermoelectric devices including traditionally used in the production are represented. There were developed models for determination of relative distribution of thermocouples number in thermoelectric device stages, the relative failure rate model, the model of relative power consumption in stages, the model of relative cooling coefficient. The comparative analysis of the basic parameters and reliability operation indicators from the maximum cooling capacity to the lowest failure rate was taken, which has showed that compared with traditional version we get a win on the failure rate by 10-20 % with a corresponding increase in the probability of thermoelectric coolers failure-free operation. These researches can be applied in the manufacture of thermoelectric cooling devices of high reliability while maintaining the value of the product.

Physicochemical Properties of Nonvariant Compositions of Ternary NaF-LiF-LnF3 Systems (Ln = La, Nd)

This paper presents results of investigations of the physicochemical properties of nonvariant compositions of ternary NaF-LiF-LnF3 systems (Ln = La, Nd) in crystalline-molten transition. The investigations have been carried out by differential thermal and X-ray phase analysis, high-temperature X-ray diffractometry, viscosimetry and thermal emf method.The ternary system NaF-LiF-LaF3 has two nonvariant points: eutectic and peritectic. The eutectic mixture of this system has the composition (mol.%): NaF(44.0)–LiF(42.0)–LaF3(14.0) and melts at 580±2°C. The peritectic has the composition (mol.%): NaF(45.0)–LiF(39.0)–LaF3(16.0) and melts at 595±2°C. Unlike the foregoing system, the ternary system NaF–LiF–NdF3 has one eutectic and two peritectics. The eutectic has the composition (mol.%): NaF(33.0)–LiF(53.0)–NdF3(14.0) and melts at 580±2°C. The peritectic, which corresponds to the formation of the compound NaNdF4, has the composition (mol.%): NaF(41.0)–LiF(44.0)– NdF3(15.0) and a melting point 595±2°C. The second peritectic has the composition (mol.%): NaF(39.0)–LiF(45.0)– NdF3(16.0) and melts at 610±2°C.An analysis of the results obtained showed that before reaching the melting temperature, the eutectic compositions of the investigated systems do not undergo structural and phase transformations. Above the melting temperature, the structure of eutectic melts is different in sprite of the very close ionic radii of rare-earth cations (rLa = 0.103 nm, rNd = 0.098 nm) and equal charges. The basis of the eutectic melt structure of the ternary LiF-NaF-LaF3 system in the range 580-700 0C is a fluoride matrix, formed by complex LaF6 3- anions. The fluorine ions around the lanthanum ions form a deformed trigonal Bernal prism. The alkali metal cations are chaotically arranged in the fluoride matrix. In the LiF-NaF-NdF3system, the fluorine ions do not form a homogeneous matrix; the melt is structurally inhomogeneous, and the neodymium cations do not form locally ordered centers with lithium and sodium polyhedra attached to them.It has been found that the plots of thermoelectric coefficient against temperature for each of the investigated nonvariant compositions have a certain temperature T, at which their slope changes its sign from negative to positive. This temperature is about 120-160°C higher than the melting temperature of the corresponding nonvariant compositions and depends on the mode of interaction of the original reactants and the nature of the compounds that are formed in this case. The reversal of the sign of the plot of thermal emf against temperature may indicate that the nature of charge carriers changes at certain temperatures.The structural inhomogeneity of the investigated compositions of the above ternary systems in the molten state is also evidenced by the results of viscosimetric studies (method of damped torsional vibration of cylinder). It has been found that as in the foregoing case, a certain characteristic temperature is typical of each of studied compositions, at which the slope of the temperature plot is reversed. Above this temperature, the plot of viscosity against temperature is satisfactorily approximated by the Arrhenius equation. This dependence of viscosity on temperature is likely due to dynamics of incongruent melting of the binary compounds NaLaF4, NaNdF4 and Na5Nd9F32.The identified characteristic temperatures on the plots of viscosity against temperature as well as on plots of coefficient of thermoelectric power against temperature increase in going from eutectic to peritectic compositions. Detected characteristic temperatures can be a sort quantitative measure of termination of incongruent decomposition of binary compounds NaLaF4, NaNdF4 and Na5Nd9F32.

Electro-Thermal and Semiconductivity Behaviour of Natural Sintered Complex Carbonate Ore for Thermo-Technological Applications

The polymetal (Zn, Pb, Fe, Ca, Mg, Cd, Ba, Ni, Ti, and SiO2) complex Umm-Gheig carbonate ore is subjected to sintering treatment at 573, 773, 973 and 1273 K respectively for four hours. Chemical, spectral, X-ray and differential thermal analyses are applied for the native ore as well as for the samples preheated and sintered. The current versus applied DC voltage (I–V) characteristics, bulk density(Db), percent shrinkage (%S), activation energy(Ea)and energy gap(Eg)are established for the sintered ore. The electrical conductivityσ, thermal conductivity (K) and thermoelectric power coefficientαhave been investigated as a function of applied temperature for the sintered ore materials. The electrical conduction is mainly achieved by free electrons near or in conduction band or n-type. As the sintering temperature(Ts)increases the conduction of the ore is also increased due to the recombination process taking place between the electrons and holes. Electrons hopping between Fe2+and Fe3+are the main charge carriers. The formation of Fe3O4at high sintering temperature acts as an active mineralizer, thus inducing an increased degree of crystallinity and a more ordered crystal structure is produced.

Transformation of the band spectrum of Hg-based HTSC and features of the temperature dependences of the thermoelectric power coefficient

The temperature variations of the thermoelectric power coefficients of the Hg-based high-temperature superconductors HgBa2Can−1CunO2n+2+δ (n = 1, 2, 3) with oxygen doping and cation substitutions are analyzed in terms of a narrow conduction band model. The parameters of the band spectrum in the vicinity of the Fermi level are determined and the manner in which they transform is examined. A correlation is found between the effective band width and the superconducting transition temperature Tc.

Effect of cobalt doping on thermoelastic martensitic transformations and physical properties of magnetic shape memory alloys Ni50 − x Co x Mn29Ga21

The magnetic and thermoelastic martensitic transformations and physical properties (magnetization, electrical resistivity, thermoelectric power, relative elongation, and thermal expansion coefficient) of multicomponent magnetic shape memory alloys Ni50 − xCoxMn29Ga21 (x = 0, 1, 2, 3, 10 at %) have been investigated. The critical temperatures of thermoelastic martensitic transformation and magnetic transitions have been determined. It has been found that the alloy with 10 at % Co undergoes a martensitic transformation in the temperature range of 6–10 K.

Crystal structure and physical properties of magnetic shape memory alloys Ni50 − x Cu x Mn29Ga21

The phase composition, crystal structure, and physical properties (magnetization, electrical resistivity, thermoelectric power, relative elongation, and thermal expansion coefficient) of the stoichiometric alloy Ni50Mn25Ga25 and nonstoichiometric alloys Ni50 − xCuxMn29Ga21 (x = 0, 1, 2) with the thermoelastic martensitic transformation have been investigated. The influence of the chemical composition on the transformations and physical properties of the alloys has been determined.

Electrical effect of introducing elemental sodium into the Bridgman melt of CuInSe2+x crystals

Transport and other measurements have been made on CuInSe2+x samples obtained from Bridgman ingots grown from melts containing controlled amounts of elemental sodium, where x represents the excess of Se over stoichiometry. Thermoelectric power and Hall coefficient at room temperature show a conductivity sign change from p- to n-type in otherwise stoichiometric CuInSe2 (x=0), with added Na between 0.2 and 0.3at%. It is further found that the critical amount of Na required to change the conductivity type, denoted by [Na]crit, increases with x, almost linearly, with an initial slope of 2, corresponding to an approximate formula of [Na]crit=2x+δ, where δ is found to be 0.25at% Na. This behavior can be accounted for quantitatively using a ‘selenium starvation’ model, whereby at the p-to-n type change, two atoms of sodium have reacted with one atom of Se to form a molecule like Na2Se, with an atom-to-atom ratio [Na]/[Se]=2. Such molecules were detected in growth run residues. However, no Na or Na compounds were detected in the interior of bulk crystals. In stoichiometric material (x=0), the crystal structure remained chalcopyrite with up to at least 3at% Na in the melt, despite the conductivity type changes. Further, no β-phase was detected in the bulk material by XRD but it was found at the surface of samples by XPS.