Increase In Thermoelectric Power Research Articles

Nanostructured Oxide (SnO2, FTO) Thin Films for Energy Harvesting: A Significant Increase in Thermoelectric Power at Low Temperature.

Previous studies have shown that undoped and doped SnO2 thin films have better optical and electrical properties. This study aims to investigate the thermoelectric properties of two distinct semiconducting oxide thin films, namely SnO2 and F-doped SnO2 (FTO), by the nebulizer spray pyrolysis technique. An X-ray diffraction study reveals that the synthesized films exhibit a tetragonal structure with the (200) preferred orientation. The film structural quality increases from SnO2 to FTO due to the substitution of F- ions into the host lattice. The film thickness increases from 530 nm for SnO2 to 650 nm for FTO films. Room-temperature electrical resistivity decreases from (8.96 ± 0.02) × 10-2 Ω·cm to (4.64 ± 0.01) × 10-3 Ω·cm for the SnO2 and FTO thin films, respectively. This is due to the increase in the carrier density of the films, (2.92 ± 0.02) × 1019 cm-3 (SnO2) and (1.63 ± 0.03) × 1020 cm-3 (FTO), caused by anionic substitution. It is confirmed that varying the temperature (K) enhances the electron transport properties. The obtained Seebeck coefficient (S) increases as the temperature is increased, up to 360 K. The synthesized films exhibit the S value of -234 ± 3 μV/K (SnO2) and -204 ± 3 μV/K (FTO) at 360 K. The estimated power factor (PF) drastically increases from ~70 (μW/m·K2) to ~900 (μW/m·K2) for the SnO2 and FTO film, respectively.

Structural and thermoelectric properties of Se doped In2Te3 thin films

The Se-Te based chalcogenides exhibit novel property of Phase Change Memory (PCM) which has potential applications in electrical non-volatile memories. These materials are also suitable in thermal to electrical energy conversions and, hence, of potential interest in energy sustainability as thermoelectric devices. In this study, the Se doped In2Te3 thin films were prepared by thermal evaporation and were annealed at 250 °C and 300 °C in Argon gas. The X-ray diffraction spectra show that thermal annealing leads to the phase transitions in Se doped In2Te3 into binary phases of In2Se3 and In2Te3. The surface morphology of the films exhibits the grains of spherical nature. Annealing also decreases the energy band gap due to the presence of two phases. From the four probe and photoconductivity measurements, a large contrast in electrical resistance between the amorphous and crystalline states is found with a variation of a few orders of magnitude. The electrical transport properties such as the electrical resistivity, Seebeck coefficient and the power factor were measured in the temperature range from 300 K to 430 K. All the deposited and annealed thin films exhibit n-type conductivity with the Seebeck coefficient ranging from -338 μVK-1 to -510 μVK-1. An increase in thermoelectric power of 25% is observed in the 300 °C annealed films in comparison to the as-deposited films. Moreover, the lower Se doped In2(Te0.96Se0.04)3 compound exhibits a better thermoelectric performance compared to the In2(Te0.90Se0.1)3 composition. This study shows the multifunctional nature of Se doped In2Te3 both for PCM and thermoelectric applications.

Effect of AC magnetic field on Al3Fe phase by measuring thermoelectric power

Effect of magnetic field on Al3Fe phase of Al-2.89 wt. % Fe alloy liquidly quenched at different temperatures has been researched. Thermoelectric power of melt in magnetic field has been measured by four-point probe technique to study thermoelectric magnetic force (TEMF) acting on Al-Fe clusters. The solid-like Al-Fe clusters are destructed and suppressed by TEMF, resulting in the primary Al3Fe phase refinement and uniform distribution, also the Fe solution decrement in primary phase. Thermoelectric power increases during treatment. The variation rate of thermoelectric power sharply increases and gradually decreases to the near zero. With the increased melt temperature, the characteristic parameters (transient ΔS, residual ΔS0 and integration of S and t) of thermoelectric power increase. Thermoelectric power reflects the melt features and transformation, attributing to the Al-Fe clusters variation affected by thermoelectric magnetic force in magnetic field.

Effect of gadolinium dopant on structural, magneto-transport, magnetic and thermo-power of Pr0.8Sr0.2MnO3

In the present investigation structural, magneto-transport, magnetic and thermo-power measurements of Gadolinium (Gd) doped Pr0.8-xGdxSr0.2MnO3 (0, 0.2, 0.25 and 0.3) manganites have been done. All the samples are single phased with orthorhombic structure. Temperature variation of resistance exhibits a high temperature transition occurring at 156 K and a low temperature cusp at around 95 K for pristine sample. With Gd doping resistance behavior shows insulating behavior throughout the whole temperature range. Magneto-Resistance (MR%) increases with Gd doping. A huge increase in thermo-electric power is observed with Gd doping.

Stretchable and flexible thermoelectric polymer composites

Polymer composites were manufactured from pristine and oxidized multi-walled carbon nanotubes and ethylene-octene copolymer. The composites had thermoelectric properties and exhibit thermoelectric effect, that is, the conversion of temperature differences into electricity. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy of the multi-walled carbon nanotubes in ethylene-octene copolymer matrix showed that the oxidation with HNO3 or KMnO4 enhanced its p-type electrical conductivity and that the thermoelectric power increase was proportional to the formation of new oxygen-containing functional groups on the surface of carbon nanotubes.

Analysis of sensing properties of thermoelectric vapor sensor made of carbon nanotubes/ethylene-octene copolymer composites

We designed a novel self-powered thermoelectric vapor sensor, whose thermogenerated voltage was modulated by chemical vapors. The sensor was made of composites of oxidized multi-walled carbon nanotubes within ethylene-octene copolymer. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy of the multi-walled carbon nanotubes within ethylene-octene copolymer showed that the oxidation with HNO3 or KMnO4 enhanced its p-type electrical conductivity and that the thermoelectric power increase was proportional to the formation of new oxygen-containing functional groups on the surface of carbon nanotubes. When this composite was subjected to a saturated vapor of either heptane (aliphatic hydrocarbon), toluene (aromatic hydrocarbon) or ethanol (alcohol), its respective relative resistance increased in average by 3.6, 1.1 and 0.05. Consequently, the magnitude of voltage generated by the thermoelectric device containing the oxidized multi-walled carbon nanotubes within ethylene-octene copolymer determined the absence or presence of the aforementioned chemical vapors.

Efficient thermoelectric energy conversion in Pb0.95Mn0.05Te p-n couple

We demonstrate an efficient energy conversion in a p-n thermoelectric couple built of bulk Pb0.95Mn0.05Te crystals grown by the Bridgman method and heavily doped n-type with Bi (n=1.9×1019cm−3) or p-type with Na (p=2.3×1019cm−3). Substitution of Mn2+ ions for Pb2+ ions at the rock-salt lattice cation sites increases the band gap of Pb1−xMnxTe and decreases the energy separation between the light hole L-band and the heavy hole Σ-band. It results in a large increase of thermoelectric power and improved thermoelectric parameters of p-type Pb1−xMnxTe. Applying the Harman method for samples of various lengths, we experimentally determined the radiation correction factors and found the thermoelectric figure of merit parameter ZT=0.75–0.8 at T=650 K for both n- and p-type materials with good thermoelectric matching of the couple. We report on thermoelectric performance of a p-n thermoelectric couple assembled of these materials and tested over the T=300–670 K temperature region.

Discussion on the electrical and thermoelectrical properties of amorphous In–Sb–Te Films

Different compositions of (In0.5Sb0.5)1−xTex (0.50 ≤ x ≤ 0.65) thin films were prepared by thermal evaporated technique, onto pre-cleaned glass substrates at ~298 K. Both dark electrical resistivity (ρ) and thermoelectric power (S) were measured in the temperature range 300–420 K. The concentration of the free carriers is obtained from DC conductivity and thermoelectric power measurements. Seebeck coefficient was found to be positive over entire temperature range, indicating that (In0.5Sb0.5)1−xTex films are p-type semiconducting materials. Also, the variation of the mobility with temperature has been estimated. Increasing tellurium concentration is found to affect the DC conductivity and thermoelectric power of the studied films. The activation energies obtained from the DC conductivity and thermoelectric power increase with increasing tellurium content. The obtained results were interpreted according to the chemical bond approach.

Electronic, thermoelectric and magnetic properties of La2NiMnO6 and La2CoMnO6

Abstract Effect of spin polarization on the electronic and thermoelectric properties of double pervoskites La 2 NiMnO 6 and La 2 CoMnO 6 are studied using the full-potential linearized augmented plane wave method. Further magnetic properties of the compound are also determined. Both compounds are indirect bandgap ferromagnetic materials. La 2 NiMnO 6 compound has a large band gap energy as compared to La 2 CoMnO 6 compound in both spin up and spin down states. The electrical conductivity, thermal conductivity and thermoelectric power increase with temperature for both the compounds in the spin up state, while the spin down state unchanged with the increase of temperature. There is no significant variation observed in Seebeck coefficient S with temperature for spin up state while the Seebeck coefficient decrease with the increase of temperature in both compounds for spin down state. The calculated total magnetic moments for both compounds reveals the strong ferromagnetic nature.

Thermoelectric performance of electrodeposited nanostructured polyaniline doped with sulfo‐salicylic acid

ABSTRACTConducting polymers, in present days, are considered to be potential thermoelectric (TE) materials. Among them polyaniline (PANI) is a promising candidate. Nanostructured polyaniline doped with organic dopant is electrodeposited and structurally characterized. Its transport properties are investigated for thermoelectric applications. The analysis of transmission electron microscopy image reveals that the sample is rod like nanostructure. This study shows that the type (inorganic/organic) of dopants plays an important role to influence the dimension of nanostructure and the electrical transport properties of PANI. In this study, organic dopant sulfosalicylic acid is proposed for enhancement of figure of merit through an increase in thermoelectric power and decrease in thermal conductivity. Compared to our earlier work the figure of merit evaluated is two orders higher than that of the inorganic dopant bismuth nitrate doped PANI. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39920.

Tuning of thermoelectric properties by embedding ErAs nanoparticles in In0.53Ga0.47As crystalline semiconductors

We theoretically analyzed the thermo electric figure of merit ZT (=S2σT/κ) which can be enhanced by nanostructuring thermoelectric materials. The key reason for increase in ZT is the reduction of thermal conductivity and increase in thermoelectric power by embedding ErAs nanoparticles in In0.53Ga0.47As crystalline semiconductors. The ErAs nanoparticles of mean diameter d = 2.4 nm are randomly distributed in the InGaAs alloy with the concentration of ErAs nanoparticles is 0.3 %. The lattice thermal conductivity and thermoelectric power were studied by incorporating the scattering of phonons with defects, grain boundaries, electrons, and phonons in the model Hamiltonian to evaluate the thermoelectric properties. We found that ErAs nanoparticles provide an additional scatterer to phonons, on inserting the nanoparticles in the crystal the phonon scattering with point defects and grain boundaries become more efficient which cause in decrease the thermal conductivity up to half and increase in thermoelectric power up to double of its value of pure crystal. The temperature- dependent of thermal conductivity and thermoelectric power are determined by competition among the several operating scattering mechanisms for the heat carriers which depends on concentration of nanoparticles in the crystal. Numerical analysis of thermoelectric properties from the present analysis will help in designing better thermoelectric materials for thermoelectric applications.

Thermoelectric studies of electronic properties of ferromagnetic GaMnAs layers

Thermoelectric power, electrical conductivity, and high field Hall effect were studied over a broad temperature range in ferromagnetic Ga(1-x)Mn(x)As epitaxial layers (0.015<x<0.06). Thermoelectric power analysis gives the information about carrier transport mechanisms in layers with both metallic and non-metallic type of conductivity and allows determination of the Fermi energy and carrier concentration. At high temperatures (T>70 K) the thermoelectric power in GaMnAs linearly increases with increasing temperature. That indicates the presence of a degenerate hole gas with the Fermi energy EF=220+-25 meV, nearly independent of Mn content (for 0.02<x<0.05). At lower temperatures GaMnAs layers with metallic-type conductivity show an additional contribution to the thermoelectric power with the maximum close to the Curie temperature. The layers exhibiting insulating electrical properties show 1/T-type increase of thermoelectric power at low temperatures.

The thermal-transport properties of theCa3−xAgxCo4O9 system (0≤x≤0.3)

Polycrystalline Ca3−xAgxCo4O9 (0≤x≤0.3) samples were prepared by solid-state reaction and their thermo-transportproperties were studied from 5 K to room temperature. With the substitution ofAg+ forCa2+, the internal chemicalpressure induced by Ag+ doping has a strong effect on the transport properties of such a strongly correlatedFermi liquid system. The electrical conductivity and the thermoelectric powerincrease simultaneously because of the enhancement of carrier concentration and thechange of carrier mobility. The thermal conductivity decreases monotonically up tox = 0.3 due tothe Ag ion acting as a rattler in the system. These results showed that the thermoelectric performanceof the Ca3Co4O9 system can be improved by doping with Ag.

Thermoelectric properties of Sn-doped TiCoSb half-Heusler compounds

Half-Heusler compounds of Sn-doped TiCoSb “TiCoSn x Sb 1− x ( x = 0.0, 0.01, and 0.05)” were prepared and their thermoelectric properties were measured above room temperature. From the EDX analysis, all the samples have three phases: the TiCoSn x Sb 1− x , Co-rich, and Ti-rich phases. The values of the thermoelectric power increase with Sn doping, and a positive thermoelectric power is obtained in the sample of TiCoSn 0.05Sb 0.95. The thermal conductivity decreases both with increasing temperature and with Sn content. The maximum value of ZT for p-type material is 0.030 at 988 K in the sample of TiCoSn 0.05Sb 0.95.

Impact of electrical resistance and TEP in layered SnSe crystals under high pressure

SnSe crystals belong to IV–VI layered binary semiconducting compound category. These layered compounds have generated a great deal of interest due to their interesting electronic properties. These electronic materials are useful because of their applications in holographic-recording systems, optoelectronics and memory switching. Earlier, several investigators have studied and reported the influence of temperature and pressure over the phase transitions in SnS and SnSe semiconductors. They also utilized Mossbauer Spectroscopy and Hydrostatic Pressure techniques to examine the bonding of the Sn atoms in SnS and SnSe. It is therefore thought worthwhile to study the effect of pressure on the thermoelectric power and the electrical resistance of SnSe crystals synthesized by a modified direct vapour transport technique. The electrical resistance has been found to be pressure dependent. The transition in electrical resistance behaviour, observed at 65 Kbar, has been explained on the basis of transition from a predominantly two-dimensional material to a more three-dimensional one. Similar to the resistance behaviour, the thermoelectric power is also found to be pressure dependent. The increase in thermoelectric power with pressure at the transition pressure of 65 Kbar has been explained. The implications are discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Cu doping and pressure effect on a layered palladium oxide: PbPdO 2

Effects of Cu doping and pressures on the physical properties of PbPdO 2 have been investigated. Single-phase samples of PbPd 1− x Cu x O 2 (0 ≤ x ≤ 0.04) have been synthesized via solid-state reaction and their temperature-dependent electrical resistivity and thermoelectric properties have been characterized. The temperature-dependent electrical resistivity exhibits a metal–insulator transition around 90–140 K for all compositions. The sign of the thermoelectric power is positive for all compositions indicating that the majority of carriers in PbPd 1− x Cu x O 2 (0 ≤ x ≤ 0.04) are holes. Both the electrical resistivity and the thermoelectric power increase as the Cu content increases. The largest power factor in this system is 0.022 μW/K 2 cm at x = 0.03. The electrical resistivity of PbPdO 2 decreases as the applied pressure increases. In addition, the metal–insulator transition is suppressed as the applied pressure increases.

Thermoelectric power of Al–Y–Ni amorphous alloys

Electrical resistivity and thermoelectric power in amorphous alloys Al 90− x Y 10Ni x ( x=0,2,5,8) are consistent with the Faber–Ziman theory when a filling of 3d states of Ni and 4d states of Y by 3p electrons of Al is included. The observed increase of thermoelectric power (TEP) during crystallization is explained taking into account the increasing content of transition metals in the amorphous matrix. Crystalline fraction is calculated from thermoelectric data.

Electrical resistivity and thermoelectric power of polycrystalline and amorphous Se-Te-Cu system

The dark electrical resistivity and thermoelectric power have been measured for the bulk ternary alloy Se-Te-Cu. The samples were both polycrystalline and amorphous in structure. The measurements were carried out below room temperature. Depending on Cu addition, crystallographic structure, and amorphous or polycrystalline state, the samples manifested semiconducting or metallic behaviour. The maximum difference in electrical resistivity magnitude was of 14 orders. The activation energy Δ E of charge carriers determined for all semiconducting samples ranged from 0.07 to 0.25 eV. An increase in thermoelectric power resulting from the electron–phonon mass enhancement was estimated.

Thermoelectric Power and Thermal Conductivity of Neutron Irradiated Superconductors YBa2Cu4O8

AbstractThe first thermoelectric investigation of fast neutron irradiated polycrystalline superconductors YBa2Cu4O8 reveals that with a rising fluence the absolute values of thermoelectric power increase gradually, the transition temperature shifts from 77 to 72 K, whereas the thermal conductivity diminishes due to the suppression of electron and phonon mean free paths by the defects created in the CuO2 layers.

Effects of sintering temperature and time on the electrical properties of pellets made from beneficiated galena ore

The effects of sintering temperature and time of PbS pellets made by cold pressing of beneficiated galena ore on the room temperature resistivity and room temperature thermoelectric power are reported. The increased resistivity of such pellets with increasing sintering time has been explained in terms of a possible reaction between PbS and PbO leading to compensation of “p”-type conductivity. The increase in thermoelectric power with sintering temperature and time has been explained on the basis of inhomogeneity in the sample following Kwok's approach.