Temperature Dependence Of Thermoelectric Power Research Articles

Lattice Dynamics of Bi1.9Dy0.1Te3 Topological Insulator

In this report, we have investigated the Density functional theory (DFT) calculation, temperature-dependent thermoelectric power and Raman spectroscopy of Bi1.9Dy0.1Te3 topological insulator (TI). In this system, discrepancy due to the rare earth ion Dy initiates a Red-shift in Raman active modes in the Bi2Te3 TI. Here, the lattice thermal conductivity (κL) was evaluated in the Umklapp scattering limit using the temperature dependency of the vibrational phonon modes and was used to evaluate the Figure of merit (ZT) of the system. It has been demonstrated that the estimated Power factor and ZT is very large, confirming the efficiency of Bi1.9Dy0.1Te3 for better thermoelectric and electronic applications. Such immense thermoelectric power value of the corresponding system was further supported by the DFT calculation.

Thermoelectric Properties of Zn Nanowires: Phonon Scattering Effect

The temperature-dependent thermoelectric power (S) of Zn nanostructures is numerically estimated using a theoretical model. The electron diffusive and phonon drag contributions to thermoelectric power are calculated within the relaxation time approximation. The phonon drag thermopower is an artifact of various operating scattering mechanisms. The anomalous behavior of (S) is successfully estimated in accordance with interaction of heat carrying phonons with impurity, grain boundaries, electrons and phonons. The scattering and transport cross sections are function of phonon frequency  in the present model and produce similar results.

Structural ordering in bulk amorphous Ge x Se 1-x samples

From temperature dependence of thermoelectric power and dc conductivity measurements [1] on bulk amorphous GexSe1-x samples (x = 10, 20, 30, 40) a dimensionless structural parameter ‘A-r/k’ was computed from intercept of thermoelectric power versus reciprocal temperature (1/T) plots. Based on ‘A-r/k’ and the slope ‘M’ of thermoelectric power versus logarithm of resistivity (ln ρ) plots, it was found that as Se content decreases, the bulk amorphous samples exhibit a transition from chalcogenides to tetrahedrally bonded amorphous semiconductors. There is a widespread agreement that tetrahedrally coordinated amorphous semiconductors crystallise at much higher temperature then the lone pair chalcogenide glasses. Therefore a decrease in Se content is considered as increase in the hardness of the samples.

Investigation on thermal and electron transport properties combined with the low-temperature scaling behaviour of strongly correlated Ce2Rh3Al9

The paper presents some new aspects of the heat transport properties and thermoelectric characteristic of the heavy fermion Kondo lattice Ce2Rh3Al9. A thorough analysis of the obtained experimental data was presented along with their detailed discussion, paying particular attention to the range of low temperatures. The temperature dependence of thermoelectric power shows large values and reveals several well formed extrema, which reflect the crystal electric field effects and the Kondo scale, respectively. The giant positive slope of the Seebeck coefficient displayed in the form of the ratio S(T)/T is observed at low temperatures. Different to the thermoelectric power, the absolute values of thermal conductivity in Ce2Rh3Al9 are quite low. In addition, we have investigated the response of thermal and electron transport on the presence of a perpendicular static magnetic field of B = 9 T. For the sake of completeness, the field dependence of the transverse magnetoresistance data recorded between 0.4 ≤ T ≤ 20 K is presented and discussed as well.

The localization effects of Gadolinium on YBCO superconductor: Thermoelectric power study

Even though the euphoria of high Tc superconductors is not that evident in recent times, the lingering taste of the field is still reminiscent. Reason for the same is the fact; the ceramics like YBCO are quite unique that paved a healthy platform for understanding variety of unconventional aspects of materials. The normal state of the YBa2Cu3O7-δ is quite unconventional that display a variety of interesting properties that include dimensionality effects, anisotropy, non-Fermi Liquid, Mott insulator derived metallic states and at times a platform for spin-charge separation and so on. In this presentation, we show results of thermoelectric effect and resistivity of Y1-xGdxBa2Cu3O7-δ that are quite indicative of multi-band effects. While the superconducting transition temperature decreases from 90 K to ∼ 80 K upon Gd substitution the normal state resistivity has increased by three times. However, the results on thermo-electric power (TEP) are quite drastic as one could observe a ten-fold increase in normal state Seebeck coefficient. Temperature dependence of thermoelectric power have been analyzed using two models of Xin and Gottwick. Physically meaningful parameters obtained using such fits include carrier concentration, Fermi energy and position of localized states etc and compared. Results are discussed in the light of evolved scenarios.

Strong temperature-dependent thermoelectric power of IrMn3 thin films of different thicknesses

IrMn3 thin films were experimentally characterized by thermoelectric power and resistivity as a function of temperature and sample thickness. The Seebeck coefficient shows strong temperature dependence and the value increases with temperature up to 350 K. An empirical Boltzmann sigmoid function can fit our data remarkably well. The temperature-dependent resistivity shows a similar behavior as the thermoelectric power, i.e. both these two properties exhibit a transitional behavior at some critical temperature range, which is further confirmed by the magnetic susceptibility measurements.

Effect of bismuth doping on the structural, magnetic, electrical, and thermopower behavior of lanthanum silver manganites

The structural, magnetic, electrical, and thermoelectric behaviors of lanthanum silver manganite and lanthanum bismuth silver manganite were thoroughly studied in the present work. Two polycrystalline samples, viz., La0.835Ag0.165MnO3 (LAMO) and La0.67Bi0.165Ag0.165MnO3 (LBAMO) possessing almost constant ratio of Mn3+/Mn4+ were synthesized using the wet chemical method. Phase formation was identified from powder X-ray diffraction and it has been confirmed through the structural analysis of which samples crystallize into rhombohedral symmetry with R-3C space group. Apparent changes at phase transition temperature were observed in temperature-dependent resistivity, magnetization and thermoelectric power behavior for bismuth-doped samples. In addition, an enhanced magnetoresistance was observed in LBAMO samples and is attributed to the presence of both ferromagnetic and anti-ferromagnetic states. The temperature-dependent resistivity data in the temperature range (50–300 K) were analyzed using the phase separation model. Spin-dependent scattering and electron–electron interactions were considered to explain the resistivity minimum in the low temperature region (T < 50 K). The Seebeck coefficient is positive and enhances around the transition temperature by substituting bismuth into LAMO. The high-temperature thermoelectric power data were explained in the framework of small polaron hopping mechanism while magnon drag effect dominates in the low temperature region.

Hopping Conduction in AgSbSe2 and (AgSbSe2)0.9(PbTe)0.1

AgSbSe2 and (AgSbSe2)0.9(PbTe)0.1 have been characterized by X-ray diffraction, differential scanning calorimetry, and temperature-dependent electric conductivity and thermoelectric power measurements in the range 80–330 K. The results demonstrate that charge transport in both materials is due to hopping of charge carriers between localized states. We have evaluated the temperature range of hopping conduction and the Fermi level density of localized states in these materials.

Effect of high energy electron beam irradiation on the structural properties, electrical resistivity and thermopower of La0.5Sr0.5MnO3 manganites

Bulk samples of La0.5Sr0.5MnO3 manganite have been subjected to electron beam irradiation of different dosages. As a consequence, the structural and electronic transport properties viz resistivity and thermoelectric power are affected to some extent. The stoichiometric content of the sample is confirmed through Energy Dispersive X-ray spectroscopy. X-ray diffraction study of the samples (unexposed and exposed to electron beam radiation) show that the samples crystallize in a single phase rhombohedral structure. Insulating behavior is displayed in the temperature range 10–300 K investigation for all the samples. Temperature dependent thermoelectric power data reveals n-type conductivity in the entire temperature zone. At high temperatures, it is concluded through detailed analysis that both resistivity and thermopower conform to small polaron hopping model. On the other hand, variable range polaron hopping model elucidates the transport characteristics at low temperatures.

Charge Transport and Thermo-emf in TlFe1−xGaxS2 Solid Solutions

TlFe1−xGaxS2 solid solutions have been prepared by direct elemental synthesis. The dependences of the thermoelectric properties and DC conductivity on temperature have been studied in TlFe1−xGaxS2 solid solutions. In terms of hopping mechanism of charge transfer, the parameters of localized states in the forbidden gap of TlFe1−xGaxS2 have been evaluated. The type of conductivity has been determined from the temperature dependences of thermoelectric power of TlFe1−xGaxS2 solid solutions.

Thermal and electron transport studies on the valence fluctuating compound YbNiAl4

We report the thermoelectric power S and thermal conductivity κ measurements on the valence fluctuating compound YbNiAl4, furthermore taking into account the impact of the applied magnetic field. We discuss our new results with revisiting the magnetic [χ(T)], transport [ρ(T)], and thermodynamic [Cp(T)] properties in order to better understand the phenomenon of thermal and electron transport in this compound. The field dependence of the magnetoresistivity data is also given. The temperature dependence of thermoelectric power S(T) was found to exhibit a similar behaviour as expected for Yb-based compounds with divalent or nearly divalent Yb ions. In addition, the values of total thermal conductivity as a function of temperature κ(T) of YbNiAl4 are fairly low compared to those of pure metals which may be linked to the fact that the conduction band is perturbed by strong hybridization. A deeper analysis of the specific heat revealed the low-T anomaly of the ratio Cp(T)/T3, most likely associated with the localized low-frequency oscillators in this alloy. In addition, the Kadowaki-Woods ratio and the Wilson ratio are discussed with respect to the electronic correlations in YbNiAl4.

Enhanced Power Factor of Single Crystalline Lead Telluride Nanowire

We present the thermoelectric properties of individual PbTe (lead telluride) nanowire (NW) grown by a stress induced method. Temperature-dependent thermoelectric power and electrical conductivity in PbTe NW with diameter 125 nm were investigated in temperature ranging of 300−400 K. The PbTe NW was found to have a Seebeck coeficient S and electrical conductivity σ of −121 μV K−1 and 138 S cm−1 at 300 K, respectively. The calculated power factor (PF) of PbTe NW (d = 125 nm) demonstrate an enhancement, wich is higher than that have been previously reported in PbTe NWs. Such an enhanced thermoelectric performance can in part be attributed to the size effect of nanowires.

Temperature-dependent structure evolution in liquid gallium

Temperature-dependent atomistic structure evolution of liquid gallium (Ga) has been investigated by using in situ high energy X-ray diffraction experiment and ab initio molecular dynamics simulation. Both experimental and theoretical results reveal the existence of a liquid structural change around 1000 K in liquid Ga. Below and above this temperature the liquid exhibits differences in activation energy for self-diffusion, temperature-dependent heat capacity, coordination numbers, density, viscosity, electric resistivity and thermoelectric power, which are reflected from structural changes of the bond-orientational order parameter Q6, fraction of covalent dimers, averaged string length and local atomic packing. This finding will trigger more studies on the liquid-to-liquid crossover in metallic melts.

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Temperature-dependent atomistic structure evolution of liquid gallium (Ga) has been investigated by using in situ high energy X-ray diffraction experiment and ab initio molecular dynamics simulation. Both experimental and theoretical results reveal the existence of a liquid structural change around 1000 K in liquid Ga. Below and above this temperature the liquid exhibits differences in activation energy for self-diffusion, temperature-dependent heat capacity, coordination numbers, density, viscosity, electric resistivity and thermoelectric power, which are reflected from structural changes of the bond-orientational order parameter Q6, fraction of covalent dimers, averaged string length and local atomic packing. This finding will trigger more studies on the liquid-to-liquid crossover in metallic melts.

Effects of negative response of electron transport to thermoelectric properties of Bi2O2Se

In thermoelectrics, the negative response of the electron transport can be observed and can block the flow of electrons leading to the reduced thermal current. As a result, the thermoelectric device’s efficiency decreases accordingly. Because of interesting properties and superior stability of Bi2O2Se at elevated temperature, it is used in this work to investigate the effects of temperature on thermoelectric properties. In the first part of calculations, density functional theory (DFT) and semiclassical Mott formula are introduced to compute density of states (DOS) and energy dependent thermoelectric properties, respectively. Then the hopping model is employed to investigate temperature-dependent thermoelectric properties, such as, electrical conductivity (σ), Seebeck coefficient (S), and power factor (PF=S2σ). The obtained results agree well with the experimental data in literature where the maximum PF=1.1×10−4W/(mK2) occurs around 800K. This investigation can provide basic knowledge and better understandings of the negative response of electron transport to temperature-dependent thermoelectric properties.

Thermoelectric power of oriented thin-film organic conductors

The temperature dependence of thermoelectric power is investigated down to low temperatures for oriented thin films of organic conductors.

Determination of parameters of a system of charge carriers in Y1–2x Ca x Pr x Ba2Cu3O y within a combined analysis of temperature dependences of thermoelectric power and Nernst–Ettingshausen coefficients

The temperature dependences of thermoelectric power S and transverse Nernst–Ettingshausen effect Q in high-temperature superconductors of the Y1–2xCaxPrxBa2Cu3Oy system with different concentrations of dopants have been investigated experimentally. It has been shown that all the specific features revealed in the behavior of the two kinetic coefficients under investigation can be described using the narrowband model with a single concept of the structure of an energy spectrum and a common set of model parameters that characterize the structure of the spectrum and properties of a system of charge carriers. Based on the quantitative analysis of the dependences S(T) and Q(T), the values of these parameters for samples of the studied composition have been determined and the character of their changes with an increase in the impurity content has been analyzed. It has been demonstrated that, for the explanation of the obtained results, it is necessary to take into account the interaction of calcium and praseodymium ions upon their simultaneous introduction into the lattice. It has been found that the mobility of charge carriers has extremely low values and almost does not depend on the level of doping, which is associated with the character of changes in the structure of the energy spectrum of Y1–2xCaxPrxBa2Cu3Oy upon doping. It has been concluded that the structure of the energy spectrum of high-temperature superconductors in the yttrium system is characterized by an asymmetry of the dispersion curve.

Role of phonon drag and carrier diffusion in thermoelectric power of polycrystalline La0.97Na0.03MnO3 manganites

We develop a theoretical model for quantitative analysis of temperature-dependent thermoelectric power of monovalent (Na) doped La0.97Na0.03MnO3 manganites. In the ferromagnetic regime, we have evaluated the phonon thermoelectric power by incorporating the scattering of phonons with impurities, grain boundaries, charge carriers and phonons. In doing so, we use the Mott expression to compute the carrier (hole) diffusion thermoelectric power (S c diff ) using Fermi energy as carrier (hole)-free parameter, and S c diff shows linear temperature dependence and phonon drag S c drag increases exponentially with temperature which is an artifact of various operating scattering mechanisms. It is also shown that for phonons the scattering and transport cross-sections are proportional to ω4 in the Rayleigh regime where ω is the frequency of the phonons. Numerical analysis of thermoelectric power from the present model shows similar results as those revealed from experiments.

Interpretation of temperature-dependent thermoelectric power behaviour of La0.67Ba0.33MnO3 manganites

The temperature dependence of the thermoelectric power S(T) in polycrystalline La0.67Ba0.33MnO3 has been investigated. In the ferromagnetic regime, the phonon thermoelectric power is evaluated by incorporating the scattering of phonons with impurities, grain boundaries, charge carriers and phonon. The Mott expression is used to compute the electron diffusive thermoelectric power (Scdiff.) using Fermi energy as electron-free parameter. The Scdiff infers linear temperature dependence and Sphdrag increases exponentially with temperature, which is an artefact of various operating scattering mechanisms. The behaviour of the S(T) is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between carrier diffusion and phonon drag contributions in the La0.67Ba0.33MnO3. Numerical analysis of thermoelectric power of the present model shows similar results as those revealed from experiments.

Strain-controlled band engineering and self-doping in ultrathin LaNiO3films

We report on a systematic study of the temperature-dependent Hall coefficient and thermoelectric power in ultra-thin metallic LaNiO$_3$ films that reveal a strain-induced, self-doping carrier transition that is inaccessible in the bulk. As the film strain varies from compressive to tensile at fixed composition and stoichiometry, the transport coefficients evolve in a manner strikingly similar to those of bulk hole-doped superconducting cuprates with varying doping level. Density functional calculations reveal that the strain-induced changes in the transport properties are due to self-doping in the low-energy electronic band structure. The results imply that thin-film epitaxy can serve as a new means to achieve hole-doping in other (negative) charge-transfer gap transition metal oxides without resorting to chemical substitution.