Large Seebeck coefficient resulting from chiral interactions in triangular triple quantum dots

We theoretically study thermoelectric transport properties through a triangular triple-quantum-dot(TTQD)structure in the linear response regime using the hierarchical equations of motion approach.It is demonstrated that large Seebeck coefficient can be obtained when properly matching the interdot tunneling strength and magnetic flux at the electron-hole symmetry point,as a result of spin chiral interactions in the TTQD system.We present a systematic investigation of the thermopower(the Seebeck coefficient)dependence on the tunneling strength,magnetic flux,and on-site energy.The Seebeck coefficient shows a clear breakdown of electron-hole symmetry in the vicinity of the Kondo regime,accompanied by the deviation from the semiclassical Mott relation in the Kondo and mixed-valence regimes,which result from the many-body effects of the Kondo correlated induced resonance together with spin chiral interactions.

A Potential Approach to Enhance the Seebeck Coefficient of UHMWPE by Using the Graphene Oxide

Thermoelectric materials have been a competent source for the production of energy in the present decade.The most important and potential parameter required for the material to have better thermoelectric characteristics is the Seebeck coefficient.In this work,ultra high molecular weight polyethylene(UHMWPE)and graphene oxide(GO)nanocomposites were prepared by mechanical mixing by containing 10000ppm,50000ppm,70000ppm,100000ppm,150000ppm,and 200000ppm loadings of graphene oxide.Due to the intrinsic insulating nature of UHMWPE,the value of Seebeck for pristine UHMWPE and its nanocomposites with 10000ppm&50000ppm of GO concentration was too low to be detected.However,the Seebeck coefficient for composites with 70000ppm,100000ppm,150000ppm,and 200000ppm loadings of GO was found to be 180,206,230,and 235μV/K,respectively.These higher values of Seebeck coefficients were attributed to the superior thermal insulating nature of UHMWPE and the conductive network induced by the GO within the UHMWPE insulating matrix.Although,the values of the figure of merit and power factor were negligibly small due to the lower concentration of charge carriers in UHMWPE/GO nanocomposites but still reported,results are extremely hopeful for considering the composite as the potential candidate for thermoelectric applications.

Optoelectronic properties and Seebeck coefficient in SnSe thin films

SnSe thin films of thickness 180 nm have been deposited on glass substrates by reactive evaporation at an optimized substrate temperature of 523 ± 5 K and pressure of 10^（-5） mbar.The as-prepared SnSe thin films are characterized for their structural,optical and electrical properties by various experimental techniques.The p-type conductivity,near-optimum direct band gap,high absorption coefficient and good photosensitivity of the SnSe thin film indicate its suitability for photovoltaic applications.The optical constants,loss factor,quality factor and optical conductivity of the films are evaluated.The results of Hall and thermoelectric power measurements are correlated to determine the density of states,Fermi energy and effective mass of carriers and are obtained as 2.8×10^（17）cm^（-3）,0.03 eV and 0.05m_0 respectively.The high Seebeck coefficient ≈ 7863 μV/K,reasonably good power factor ≈7.2×10^（-4） W/（m·K^2） and thermoelectric figure of merit ≈1.2 observed at 42 K suggests that,on further work,the prepared SnSe thin films can also be considered as a possible candidate for cryogenic thermoelectric applications.

Synthesis,Electrical Conductivity and Seebeck Coefficient of La_(0.9)A_(0.1)FeO_3(A=Mg,Ca,Sr,Ba)

Lanthanum ferrites ceramics La0.9A0.1FeO3 （A=Mg, Ca, Sr, Ba） have been prepared by solid state reaction. X-ray power diffraction analysis reveals that all samples are of pure perovskite structure with orthorhombic phase. Electrical conductivity and Seebeck coefficient have been measured in vacuum within the temperature range between room temperature and 800℃. The electrical conductivity shows semiconducting behavior. Temperature dependence of electrical conductivity indicates that adiabatic small-polaron hopping mechanism is dominant for their electric transportations. Seebeck coefficients are positive for samples, suggesting ptype conduction in the whole temperature range. The highest Seebeck coefficient is found to be 654 μV/K for La0.9A0.1FeO3. Except La0.9A0.1FeO3, the electrical conductivity of La0.9A0.1FeO3 increases with increasing atomic number of the A-site element, while Seebeck coefficient decreases.

Thermal and Electrical Properties of Liquid Metal Gallium During Phase Transition

Liquid metal gallium has been widely used in numerous fields, from nuclear engineering, catalysts, and energy storage to electronics owing to its remarkable thermal and electrical properties along with low viscosity and nontoxicity. Compared with high-temperature liquid metals, room-temperature liquid metals, such as gallium(Ga), are emerging as promising alternatives for fabricating advanced energy storage devices, such as phase change materials, by harvesting the advantageous properties of their liquid state maintained without external energy input. However, the thermal and electrical properties of liquid metals at the phase transition are rather poorly studied, limiting their practical applications. In this study, we reported on the physical properties of the solid–liquid phase transition of Ga using a custom-designed, solid–liquid electrical and thermal measurement system. We observed that the electrical conductivity of Ga progressively decreases with an increase in temperature. However, the Seebeck coefficient of Ga increases from 0.2 to 2.1 μV/K, and thermal conductivity from 7.6 to 33 W/(K·m). These electrical and thermal properties of Ga at solid–liquid phase transition would be useful for practical applications.

Effect of Polyaniline/manganese Dioxide Composite on the Thermoelectric Effect of Cement-based Materials

To enhance the thermoelectric effect of cement-based materials,conductive polyaniline(PANI)modified MnO_(2)powder was synthesized and used as a thermoelectric component in the cement composites.The nanostructured PANI was deposited on the surface of the nanorod-shapedα-MnO_(2)particle and the weight ratio of PANI to MnO_(2)was 22.3:77.7 in the composite.The synthesized PANI/MnO_(2)composite was nanostructured according to the SEM image.The test results of the thermoelectric properties proved that the PANI/MnO_(2)composite was effective as the Seebeck coefficient and electrical conductivity values of the cement composites with PANI/MnO_(2)inside were 3-4 orders of magnitude higher than those of pure cement paste and the thermal conductivity values of these cement samples were similar.The obtained maximum figure of merit(ZT)value(2.75×10^(-3))was much larger than that of conductive materials reinforced cement-based composites.The thermoelectric effect of cement composites is mainly enhanced by the increased Seebeck coefficient and electrical conductivity in this work.

Preparation and thermoelectric properties of ternary rare earth sulfide γ-Ce_(3–x)Eu_xS_4

The effect of Eu-substitution on the density and thermoelectric properties of ternary sulfide Ce3-xEuxS4 （0≤x≤0.8） compacts was investigated. Ce3-xEuxS4 powders were prepared via the sulfurization of the oxide using CS2 gas at 1473 K. The pressureless sintered Ce3-xEuxS4 compacts in the atmosphere were crystallized in the T-phase. The density of the Ce3-xEuxS4 compacts increased with the increasing of Eu-substitution. Eu-substitution yielded a higher Seebeck coefficient and lower electrical resistivity. The highest value of the thermoelectric power factor of 1.41×10^-4 W/K^2m was obtained for the Ce2.2Eu0.8S4 compact at 673 K. It indicated that Eu-substitution was effective for improving thermoelectric properties of Ce3-xEuxS4.

High-temperature Electric Properties of Polycrystalline La-doped CaMnO_3 Ceramics

Polycrystalline La-doped CaMnO3 ceramics have been prepared by a solid-state sintering method. Analysis of microstructure and phase composition indicates that the addition of La can prohibit the further growth of grain, and no impurity phase appears. The results revealed that the La doping can lead to a large change of the activation energy （from 0.2：2 to 0.02 eV）, and thus result in a marked increase in electric conductivity of 2-4 orders of magnitude. The power factor can reach about 1.5×10-4 W.m-1.K-2 in a wide temperature range, which potentially make them attractive for n-type high-temperature thermoelectric materials.

Synthesis and Thermoelectric Properties of Polyaniline

Electrical conductivity and seebeck coefficient at different temperatures,and thermal conductivity at room temperature for various doped polyaniline (PAn) samples were measured,and the thermoelectric figure of merit ZT was calculated.The effects of preparation methods and temperature on thermoelectric properties were discussed.The results show that the electrical conductivity and the seebeck coefficient of PAn are strongly dependent on the preparation conditions and temperature.The electrical conductivity becomes larger and the seebeck coefficient becomes smaller as PAn molecular weight increases.Redoping by organic acid and HCl results in an increase in both electrical conductivity and Seebeck coefficient of PAn,and therefore ZT value.The electrical conductivity increases and the seebeck coefficient decreases as the temperature increases when T<T d (dedoping temperature).The decreasing of the electrical conductivity and increasing of the seebeck coefficient take place by dedoping when T>T d.The thermal conductivity is lower,and insensitive to the sample preparation conditions.

Synthesis and Thermoelectric Properties of Ca_(2.6)Nd_ ( 0.4)Co_4O_9 Compound

The layered cobaltite Ca 2.6Nd 0.4Co 4O 9 was synthesized by the solid-state reaction. Their crystal structure was determined by the X-ray powder diffraction and CELL program. The prepared Ca 2.6Nd 0.4Co 4O 9 compound has the monoclinic symmetry. The electrical conductivity and Seebeck coefficient were measured from room temperature to 700 ℃ in air. Both the properties increase while rising temperature. The thermoelectric power of Ca 2.6Nd 0.4Co 4O 9 is about 242 4 μV·K -1. The results imply a promising way to enhance the thermoelectric properties of the layered cobaltite oxides by optimizing their composition and microstructure.

Thermospin effects in parallel coupled double quantum dots in the presence of the Rashba spin-orbit interaction and Zeeman splitting

The thermoelectric and the thermospin transport properties, including electrical conductivity, Seebeck coefficient, thermal conductivity, and thermoelectric figure of merit, of a parallel coupled double-quantum-dot Aharonov-Bohm interferometer are investigated by means of the Green function technique. The periodic Anderson model is used to describe the quantum dot system, the Rashba spin-orbit interaction and the Zeeman splitting under a magnetic field are considered. The theoretical results show the constructive contribution of the Rashba effect and the influence of the magnetic field on the thermospin effects. We also show theoretically that material with a high figure of merit can be obtained by tuning the Zeeman splitting energy only.

Synthesis and thermoelectric properties of Bi-doped SnSe thin films

Bi doped n-type SnSe thin films were prepared by chemical vapor deposition(CVD)and their structure and thermoelectric properties were studied.The x-ray diffraction patterns,x-ray photoelectron spectroscopy,and microscopic images show that the prepared SnSe thin films were composed of pure SnSe crystals.The Seebeck coefficients of the Bi-doped SnSe were greatly improved compared to that of undoped SnSe thin films.Specifically,Sn_(0.99)Bi_(0.01)Se thin film exhibited a Seebeck coefficient of905.8μV·K^(-1) at 600 K,much higher than 285.5μV·K^(-1) of undoped SnSe thin film.Further first-principles calculations reveal that the enhancement of the thermoelectric properties can be explained mainly by the Fermi level lifting and the carrier pockets increasing near the Fermi level due to Bi doping in the SnSe samples.Our results suggest the potentials of the Bi-doped SnSe thin films in thermoelectric applications.

Vanadium based XVO3 (X=Na, K, Rb) as promising thermoelectric materials: First-principle DFT calculations

We investigate structural,mechanical,thermodynamic,and thermoelectric properties of vanadium-based XVO3(X=Na,K,Rb)materials using density functional theory(DFT)based calculations.The structural and thermodynamic stabilities are probed by the tolerance factor(0.98,1.01,and 1.02)with the negative value of enthalpy of formation.Mechanical properties are analyzed in the form of Born stability criteria,ductile/brittle nature(Poisson and Pugh's ratios)and anisotropy factor.To explore the electronic transport properties,we study the electrical conductivity,thermal conductivity,Seebeck coefficient and power factor in terms of chemical potential and temperature.High values of Seebeck coefficient at room temperature may find the potential of the studied perovskites in thermo-electrics devices.

Thermoelectric Properties of Czochralski GeSi Crystal

In order to discuss the application possibility of SiGe crystal in thermoelectric materials, we investigated the thermoelectric properties of several silicon-germanium alloys with different content, orientation and electric conductive type. As discussed in the experiment result, the absolute value of Seebeck coefficient fluctuates from 300 to 600 μV/K in the whole temperature range. In the present paper, the relationship of Seebeck coefficient against content, orientation and electric conductive type is summarized in detail. The Seebeck coefficient of the sample with 〈111〉 orientation is smaller than that in 〈100〉 at the same temperature. Absolute value of P-type is larger than that of N-type except pure Ge. But as the temperature increases, the absolute value of pure Ge decreases many times as quickly as that of other specimens. In addition, the specimens of bulk GeSi alloy crystals for experiment were grown by the Czoehralski method through varying the pulling rate during the growing process.

Optical and electrical properties of InGaZnON thin films

The substrate temperature(Ts)and N2 partial pressure(PN2)dependent optical and electrical properties of sputtered InGaZnON thin films are studied.With the increased Ts and PN2,the thin film becomes more crystallized and nitrified.The Hall mobility,free carrier concentration(Ne),and electrical conductivity increase with the lowered interfacial potential barrier during crystal growing.The photoluminescence(PL)intensity decreases with the increased Ne.The band gap(Eg)narrows and the linear refractive index(n1)increases with the increasing concentration of N in the thin films.The Stokes shift between the PL peak and absorption edge decreases with Eg.The n1,dispersion energy,average oscillator wavelength,and oscillator length strength all increase with n1.The single oscillator energy decreases with n1.The nonlinear refractive index and third order optical susceptibility increase with n1.The Seebeck coefficient,electron effective mass,mean free path,scattering time,and plasma energy are all Ne dependent.

Improved thermoelectric property of cation-substituted CaMnO_3

Single-phase pristine and cation-substituted calcium manganite（Ca1-xBixMn1-yVyO3-δ） polycrystalline samples were synthesized by the solid state reaction technique. Their thermoelectric properties were measured by a set up that was designed and assembled in the laboratory. The Ca1-x BixMn1-yVyO3-δsample with x = y = 0.04 has shown a power factor（S^2σ） of 176 μW/m/K^2 at 423 K, which is nearly two orders of magnitude higher than that of the pristine sample（2.1 μW/m/K2）. The power factor of the substituted oxide remains almost temperature independent as the Seebeck coefficient increases monotonically with temperature, along with the simultaneous decrease in electrical resistivity which is attributed to enhanced electron density due to co-doping of bismuth and vanadium and grain boundary scattering. These cation-substituted calcium manganites can be used as a potential candidate for an n-type leg in a thermoelectric generator（module）.

Thermoelectric Properties of ZnO-P2O5/(Ni) Composites

The overall purpose of the present study is basically to understand the manifestation of the thermo-electrical properties of the matrix ZnO-P2O5 first, and of the ZnO-P2O5 composites loaded with different volume fractions of nickel (Ni) as conductive fillers. In the matrix ZnO-P2O5, the values of electrical conductivity varied between 1.14 × 10-8 and 7.8 × 10-7 (S/cm), and the Seebeck coefficient value varied between minimal value 265 and maximal value 670 (μV/K) in the studied temperature. In composite ZnO-P2O5/Ni, it was shown that the Seebeck coefficient changed from high positive to negative values when the filler amount was increased, indicating a non-conducting to conducting phase transition. Such behavior exhibits that this transition is accompanied by the passing of carrier charge from p to n type. The study of thermoelectrically transport for high volume fraction of filler enabled the achievement, for the first time on this kind of composites, of an original transition called PTC transition. Thus, highest values of power factor (PF = S2 ≈ 2 × 10-3 W·m-1·K-2 at 407 K) were obtained, giving a possibility of industrial applications.

Flexible thermocouple using a thermoelectric graphene fiber with a seamless junction

Temperature is an important physical variable that indicates the condition of the human body and artificial systems.Advanced wearable applications require the development of temperature sensors with different form factors.In this study,a fiber-shaped thermoelectric temperature sensor is fabricated using a continuous graphene fiber whose two halves possess different reduction states.A seamless junction is formed by partially reducing a wet-spun graphene oxide fiber with hydroiodic acid(HI)solutions of different concentrations.One-half of the fiber is mildly reduced with 0.97 wt%HI,while the other half is highly reduced with 30.6 wt%HI.The different reduction states of the graphene composite fiber result in different Seebeck coefficients,allowing for the fabrication of a fiber-shaped graphene thermocou-ple without any laborious assembly.The flexible graphene thermocouple exhibits high sensitivity with a thermopower of 12.5μV K^(-1)in the temperature range of room temperature to∼70℃.Furthermore,it exhibits high linearity with a correlation coefficient exceeding 0.995 and fast response with a time constant of 0.24 s.Owing to its mechanical robustness and flexibility,the stand-alone graphene ther-mocouple can be knitted into a cotton fabric glove,which presents a fast response to environmental changes without any external power source.This work offers a unique fabrication method for producing a high-performance,flexible thermocouple that features a seamless and clear junction without the use of additional materials.This alternative method eliminates the complicated assembly processes typically required for conventional thermocouples.

Spin-dependent transport properties and Seebeck effects for a crossed graphene superlattice p-n junction with armchair edge

Using the nonequilibrium Green＇s function method combined with the tight-binding Hamiltonian, we theoretically investigate the spin-dependent transmission probability and spin Seebeck coefficient of a crossed armchair-edge graphene nanoribbon （AGNR） superl＇attice p-n junction under a perpendicular magnetic field with a ferromagnetic insulator, where junction widths Wi of 40 and 41 are considered to exemplify the effect of semiconducting and metallic AGNRs, respectively. A pristine AGNR system is metallic when the transverse layer m = 3j ＋ 2 with a positive integer j and an insulator otherwise. When stubs are present, a semiconducting AGNR junction with width W1= 40 always shows metallic behavior regardless of the potential drop magnitude, magnetization strength, stub length, and per- pendicular magnetic field strength. However, metallic or semiconducting behavior can be obtained from a metallic AGNR junction with Wi = 41 by adjusting these physical parameters. Furthermore, a metal-to-semiconductor transition can be obtained for both superlattice p-n junctions by adjust- ing the number of periods of the superlattice. In addition, the spin-dependent Seebeck coefficient and spin Seebeck coefficient of the two systems are of the same order of magnitude owing to the appearance of a transmission gap, and the maximum absolute value of the spin Seebeck coefficient reaches 370 μV/K when the optimized parameters are used. The calculated results offer new possi- bilities for designing electronic or heat-spintronic nanodevices based on the graphene superlattice p-n junction.

Optimization of thermoelectric properties of n-type Bi_2(Te,Se)_3 with optimizing ball milling time

The thermoelectric properties at elevated temperature were investigated for n-type Bi2（Te,Se）3 which is obtained from ball milling processed powder with various milling times. Electrical properties such as electrical resistivity and Seebeck coefficient are clearly dependent on milling time, in which the carrier concentration is attributed to the change of the electrical properties. The concentrations of the defects are also varied with the ball milling time, which is the origin of the carrier concentration variation. Even though finer grain sizes are obtained after the long ball milling time, the temperature dependence of the thermal conductivity is not solely understood with the grain size, whereas the electrical contribution to the thermal conductivity should be also considered. The highest figure of merit value of ZT = 0.83 is achieved at 373 K for the optimized samples, in which ball milling time is 10 h. The obtained ZT value is 48% improvement over that of the 0.5-h sample at 373 K.