Absolute Value Of Seebeck Coefficient Research Articles

Thermoelectric properties of KCaF3

Using first-principles calculations based on density functional theory (DFT) with generalized gradient approximation (GGA), the electronic and thermoelectric properties of KCaF3 are calculated. The electronic structure calculated with GGA shows that KCaF3 is an insulator. The thermoelectric properties of KCaF3 are computed as a function of chemical potential μ and charge carrier concentrations (1018–1022 cm−3). Both hole and electron doping decrease the absolute value of Seebeck coefficient. The calculated power factor shows that p-type KCaF3 has a larger power factor at the optimized charge carriers. The maximum figure of merit (ZT) occurs around 1021 cm−3 hole carrier concentrations and the largest value of ZT ∼0.7 is achieved at 800 K. When KCaF3 is doped with electron, the maximum ZT occurs around 1020 cm−3 and the largest value of ZT at 800 K is about 0.4. Hence, high ZT in KCaF3 is possible at high hole carrier concentrations as compared with electron carrier concentrations. Compared with n-type KCaF3, p-type KCaF3 has good thermoelectric properties, which are attributed to larger effective mass and low thermal conductivity of holes.

Formation mechanism and thermoelectric properties of CaMnO3 thin films synthesized by annealing of Ca0.5Mn0.5O films

A two-step synthesis approach was utilized to grow CaMnO3 on M-, R- and C-plane sapphire substrates. Radio-frequency reactive magnetron sputtering was used to grow rock-salt-structured (Ca, Mn)O followed by a 3-h annealing step at 800 °C in oxygen flow to form the distorted perovskite phase CaMnO3. The effect of temperature in the post-annealing step was investigated using x-ray diffraction. The phase transformation to CaMnO3 started at 450 °C and was completed at 550 °C. Films grown on R- and C-plane sapphire showed similar structure with a mixed orientation, whereas the film grown on M-plane sapphire was epitaxially grown with an out-of-plane orientation in the [202] direction. The thermoelectric characterization showed that the film grown on M-plane sapphire has about 3.5 times lower resistivity compared to the other films with a resistivity of 0.077 Ωcm at 500 °C. The difference in resistivity is a result from difference in crystal structure, single orientation for M-plane sapphire compared to mixed for R- and C-plane sapphire. The highest absolute Seebeck coefficient value is − 350 µV K−1 for all films and is decreasing with temperature.

HPHT synthesis and enhanced TE performance of Te and Sn/Se elements binary-doped CoSb3

A series of binary-doped CoSb3 with Te and Se/Sn bulk compounds Co4Sb[Formula: see text]TexSny/Sey ([Formula: see text] and 0.6, [Formula: see text] and 0.3), have been successfully prepared via a simple high pressure and high-temperature (HPHT) method. And, the influence of the doping elements on the microstructure of the samples synthesized under diverse pressures and the corresponding TE performance were studied in detail. Comparing with other preparation methods, the synthesis time of HPHT was acutely shortened. The obtained samples contain more grain boundaries, lattice disorder, dislocations and the possible “nanodot”, which have positive effect on reducing thermal conductivity. The experimental data indicate that the absolute values of Seebeck coefficient increases with pressure. What’s more, the thermal conductivities show a monotone decreasing trend as the synthesis pressure rises. The minimum value obtained is 1.93[Formula: see text]Wm[Formula: see text]K[Formula: see text] at normal temperature for Co4Sb[Formula: see text]Te[Formula: see text]Se[Formula: see text] prepared under 3[Formula: see text]GPa.

Insight into structural, electronic and thermoelectric properties of Zr2MnX (X = Ga, In) Heuslers

Spin polarized analysis of band structure, magnetism and thermoelectric properties of Zr2MnX (X = Ga, In) alloys have been carried out within DFT and post-DFT techniques. The structural properties show the F-43m phase as the stable phase with optimized lattice parameters as 6.58 and 6.69 Å, respectively. The band structure calculation shows spin gapless semiconducting behavior with negligible magnetic moments according to Slater-Pauling rule. The transport properties were investigated to find the stand of alloys for thermoelectric use. Seebeck coefficient variation define them as n-type materials, with descent value of electrical conductivity. The absolute values of Seebeck coefficient found at room temperatures are 35.54 μV K−1 and 32.93 μV K−1. The power factor variation was used to check the efficiency, which varies from 0.92(0.04) × 10−4 W K−2 m at 50 K to 12.53(7.0) × 10−4 W K−2 m at 500 K, respectively for Zr2MnX (X = Ga, In). The overall peculiar electronic behavior together with thermoelectric efficiency finds their applications in spintronics and room temperature waste heat recovery systems.

The thermoelectric properties of the Mg2(Sn,Si) films by magnetron sputtering with different microstructure

The Mg2(Si,Sn) solid solutions films have been deposited on single crystalline Si(111) substrates under temperatures from 130 to 400 °C by magnetron sputtering using a Mg-Si-Sn alloy target. The phase components, microstructures and the thermoelectric properties of these films were investigated. It is indicated that the films deposited under lower temperature (≤300 °C) possess a cubic anti-fluorite structure phase and their structures transform into orthorhombic and hexagonal with the increasing temperature to 400 °C. Meanwhile, the tetragonal structure metal Sn phase occurs on samples deposited under temperatures of 350 °C and 400 °C. Furthermore, the film deposited under 350 °C is composed of cubic anti-fluorite structure and orthorhombic structure phase, and possesses the highest absolute value of Seebeck coefficient and the highest electrical resistivity. On the other hand, the film deposited under 130 °C which is composed of only cubic anti-fluorite structure possesses the highest power factor at all measured temperature due to higher absolute value of Seebeck coefficient and lower electrical resistivity. It is suggested that the Mg2(Si,Sn) solid solutions film with cubic phase structure has higher power factor than that with orthorhombic and hexagonal phase structure.

Thermoelectric Properties of Bi-Doped Magnesium Silicide Stannides.

Mg2(Si,Sn)-based compounds have shown great promise for thermoelectric (TE) applications, as they are nontoxic and comprised abundantly available constituent elements. In this work, the crystal structures and TE properties of polycrystalline materials with nominal compositions Mg2Si0.35Sn0.65- xBi x ( x = 0, 0.015, 0.030, and 0.045) and Mg2Si ySn0.97- yBi0.03 ( y = 0.30, 0.325, and 0.35) have been investigated. The electrical conductivity, Seebeck coefficient, and thermal conductivity are strongly affected by the presence of Bi. Undoped samples showed higher values of Seebeck coefficients (below 600 K), lower electrical conductivity, and lower thermal conductivity (above 600 K) in comparison to the Bi-doped samples. Furthermore, the signs of Seebeck coefficients are all negative, confirming that n-type conduction is dominant in these materials. Electrical conductivity was enhanced by increasing the Bi content up to 3% on the Si/Sn site because of the increasing amount of electron donors, and the absolute value of Seebeck coefficient decreased. When the Bi content is greater than 3%, lower zT values were obtained at 773 K. Thermal conductivity values might decrease with increasing Sn alloying for Mg2Si ySn0.97- yBi0.03, as mass and strain fluctuation caused by alloying can effectively scatter phonons. However, a different behavior was observed in higher Sn content material, possibly because of the absence of Mg atoms at the interstitial site [Mgi, on (1/2, 1/2, 1/2)] and vacancies of Mg atoms at the (1/4, 1/4, 1/4) site, as confirmed by Rietveld refinements. Outstanding figure of merit values in excess of unity were achieved with all samples, culminating in zTmax = 1.35.

Thermoelectric Properties of Co- and Mn-Doped Al2Fe3Si3

Al2Fe3Si3 is a promising semiconductor for application as an environmentally friendly thermoelectric material. Its intrinsic carrier concentration is 5 × 1019 cm−3 and shows p-type conduction. In this article, we report on the thermoelectric properties of carrier-doped Al2Fe3Si3. Co or Mn was substituted for Fe for electron or hole doping, respectively. Al2Fe3−xMxSi3 (M=Co or Mn; x = 0.1–1.0 for Co and 0.1–0.3 for Mn) samples were synthesized by arc melting followed by spark plasma sintering and heat treatment. The Co- and Mn-doped samples displayed Hall carrier concentrations of 1.4 × 1020 cm−3 to 5.1 × 1020 cm−3 for n-type and 1.3 × 1020 cm−3 to 1.3 × 1021 cm−3 for p-type conduction. The n-type Al2Fe3Si3 exhibited a higher absolute value of Seebeck coefficient and lower Hall carrier mobility than p-type Al2Fe3Si3 at the same carrier concentration. The power factor increased with increasing carrier concentration for n-type conduction, and reached 0.65 × 10−3 W/mK at 520 K. On the other hand, the power factor for p-type Al2Fe3Si3 was not enhanced with increasing carrier concentration. The maximum ZT value for Co-substituted Al2Fe3Si3 was 0.09 at 600 K, which is 50% higher than that of pure Al2Fe3Si3.

Enhancement of thermoelectric properties by fluorine doping in [formula omitted

The transport and thermoelectric properties of the LaO1−xFxBiPbS3 compounds are studied. On the transport part, fluorine doping effectively reduces the electrical resistivity, and transforms the transport behavior from semiconducting-like to metallic-like. An evident enhancement of thermoelectric performance (power factor) is achieved in LaO0.6F0.4BiPbS3, with an obviously larger absolute value of Seebeck coefficient (|S|) compared to the parent compound. Hall coefficient measurements reveal the depression of effective carrier density for all the doped samples at high temperatures. The present results suggest that electron carriers alone can not explain the improvement of thermoelectric properties by fluorine doping, the conduction of ionic carriers should be taken into account.

Effects of sintering temperature on the microstructure and thermoelectric properties of mesostructured Co4Sb11.5Te0.5 skutterudites dispersed nano-TiN

The mesostructured skutterudites Co4Sb11.5Te0.5 + nano-TiN composites are prepared through ball milling and spark plasma sintering (SPS). The influence of the various SPS temperatures within the range of 813–933 K on the microstructure and thermoelectric properties are focus in this work. The average grain sizes of the skutterudites increase from ~ 110 to ~ 500 nm with the increasing SPS temperature, while the densities of composites decrease from 7.02 to 6.26 g cm−3. Additionally, the phase of CoTe2 is detected in the samples sintered at 903–933 K. With the SPS temperature increasing from 813 to 903 K, the electrical conductivity and thermal conductivity increase simultaneously, and then decrease when SPS temperature rises to 933 K. The absolute value of Seebeck coefficient shows no clear changes when SPS temperature is not higher than 873 K but then slightly decreases with the increasing of SPS temperature. At last, the optimum SPS temperature is determined as 873 K, the ZT value of 1.07 at 800 K for the sample SPSed at 873 K is obtained, which is 11.5% higher than that of the sample SPSed at 903 K.

Thermoelectric and Transport Properties of FeV1−xTixSb Half-Heusler System Synthesized by Controlled Mechanical Alloying Process

The thermoelectric and transport properties of Ti-doped FeVSb half-Heusler alloys were studied in this study. FeV1−xTixSb (0.1 < x < 0.5) half-Heusler alloys were synthesized by mechanical alloying process and subsequent vacuum hot pressing. After vacuum hot pressing, a near singe phase with a small fraction of second phase was obtained in this experiment. Investigation of microstructure revealed that both grain and particle sizes were decreased on doping which would influence on thermal conductivity. No foreign elements pick up from the vial was seen during milling process. Thermoelectric properties were investigated as a function of temperature and doping level. The absolute value of Seebeck coefficient showed transition from negative to positive with increasing doping concentrations (x ≥ 0.3). Electrical conductivity, Seebeck coefficient and power factor increased with the increasing amount of Ti contents. The lattice thermal conductivity decreased considerably, possibly due to the mass disorder and grain boundary scattering. All of these turned out to increase in power factor significantly. As a result, the thermoelectric figure of merit increased comprehensively with Ti doping for this experiment, resulting in maximum thermoelectric figure of merit for FeV0.7Ti0.3Sb at 658 K.

Microstructure characterization and thermoelectric properties of Sr0.9La0.1TiO3 ceramics with nano-sized Ag as additive

Sr0.9La0.1TiO3 thermoelectric ceramics with different contents of nano-sized Ag metal particles as additive were prepared by conventional solid state reaction method, and the influences of Ag adding content on the microstructure and thermoelectric properties were investigated. XRD characterization confirmed that the main phase was perovskite Sr0.9La0.1TiO3, along with a small amount of metal Ag phase. SEM images showed that all of the samples were dense, and the results of TEM indicated that the Ag particles accumulated at the grain boundaries to form a percolating network, contributing to increasing the electrical conductivity. Raman spectra of Sr0.9La0.1TiO3/xAg samples before and after annealing in Ar+C atmosphere showed a great difference, resulting from the creation of oxygen vacancies and changes in the TiO bond vibration and rotation mode. With increasing Ag adding content, the absolute value of Seebeck coefficient increased. Ag addition caused an increase in carrier concentration and acted as electrical connections between the grains, which improved the electrical conductivity and reduced the thermal conductivity to 1.4–3.4 W/m/K. Finally, the maximum ZT value of ZT883K = 0.30 was obtained for x = 20 wt% samples.

The enhanced thermoelectric properties of BiMnO3 ceramics by Sr-doped

A series of Bi1−xSrxMnO3 (x = 0.40, 0.45, 0.50, 0.55) samples labeled as BSMO040, BSMO045, BSMO050, and BSMO055, respectively, have been fabricated by the modified solid-state reaction method. The crystal structural, microstructures, and chemical states of the elements and the thermoelectric properties were investigated with respect to the partial substitution of Sr2+ for Bi3+. The samples were characterized by x-ray diffraction (XRD) at 723 K, scanning electron microscopy (SEM), and x-ray photoelectron spectroscopy (XPS). Moreover, their electrical conductivities (σ), Seebeck coefficients (S), and thermal conductivities (κ) were determined. All the samples exhibited orthorhombic structure. The partial substitution of Sr2+ for Bi3+ caused valence shift of some Mn ions from +3 to +4 to maintain electric charge balance. The change in electric charge led to an increase in electron concentration, and thus, the electrical conductivity as well as the absolute value of Seebeck coefficient increased. Consequently, the power factor also increased. The highest power factor (0.3 × 10−4 Wm−1 K−1) was obtained for BSMO055 at 1023 K. Moreover, the highest dimensionless figure-of-merit (ZT) obtained in this study was 0.015 for BSMO055 at 1073 K. It can be concluded that the partial substitution of Sr2+ for Bi3+ in the Bi1−xSrxMnO3 samples (x = 0.40, 0.45, 0.50, and 0.55) improved the thermoelectric properties effectively.

Thermoelectric Properties of the Perovskite-Type Oxide SrTi1−xNbxO3 Synthesized by Solid-State Reaction Method

The perovskite-type oxide materials SrTi1−xNbxO3 (X = .02, 0.03, 0.04, 0.05 and 0.06) were synthesized by the conventional solid-state reaction method and the thermoelectric properties in terms of Nb doping at the B-site in the oxides were investigated in this study. The formation of single phase cubic perovskite structure was confirmed by the powder X-ray diffraction analysis. Negative conduction is shown in this materials system. The absolute value of Seebeck coefficient increased with increasing temperature over the measured temperature. The electrical conductivity decreased monotonically with increasing temperature, showing degenerating conduction behavior. The thermal conductivity, k, generally decreased with increasing temperature. The power factor increased with increasing Nb-doping level up to 5.0 mol% and hence the dimensionless figure of merit ZT, increased up to 5.0 mol%. The maximum ZT value was observed for SrTi0.95Nb0.05O3 at 873 K.

Synthesis and Thermoelectric Properties of Ni-Doped ZrCoSb Half-Heusler Compounds

The Ni-doped ZrCo1−xNixSb half-Heusler compounds were prepared by arc-melting and spark plasma sintering technology. X-ray diffraction analysis results showed that all samples were crystallized in a half-Heusler phase. Thermoelectric properties of ZrCo1−xNixSb compounds were measured from room temperature to 850 K. The electrical conductivity and the absolute value of Seebeck coefficient increased with the Ni-doping content increasing due to the Ni substitution at Co. sites. The lattice thermal conductivity of ZrCo1−xNixSb samples was depressed dramatically because of the acoustic phonon scattering and point defect scattering. The figure of merit of ZrCo1−xNixSb compounds was improved due to the decreased thermal conductivity and improved power factor. The maximum ZT value of 0.24 was achieved for ZrCo0.92Ni0.08Sb sample at 850 K.

Preparation and thermoelectric properties of mixed valence compound Sn2S3

The preparation and thermoelectric properties of Sn2S3 polycrystalline samples were reported. An almost single-phase Sn2S3 polycrystalline sample was obtained by heating Sn and S mixed powders: the sample was successfully densified using a spark-plasma-sintering method. Sn2S3 building blocks with electron lone pairs were weakly bonded via van der Waals force. Similar to other compounds with electron lone pairs, a thermal conductivity lower than 1.4 W·m−1·K−1 was obtained for the Sn2S3 sample from 298 to 701 K. Although the Sn2S3 sample exhibited a high absolute value of Seebeck coefficient, its electrical conductivity was considerably low, leading to a low dimensionless figure of merit, zT, of 9.6 × 10−4 at 700 K. The poor electrical transport properties indicated that the Sn2S3 sample was a semiconductor with an extremely low carrier density, which was confirmed by measurements of its band gap and by calculations of the temperature dependence of Seebeck coefficient.

Bi2Te3 thin hexagonal nanoplatelets: Synthesis and its characterization studies

Solvothermal synthesis and optimization of pure Bismuth telluride (Bi2Te3) hexagonal nanoplatelets was carried out from Bismuth Oxide (Bi2O3) and Tellurium dioxide (TeO2). XRD measurements revealed a sensitive change in crystallization behaviour in correlation with variation in Te/Bi stoichiometry identified through the exchange in intensities between (1010̅) and (110) peaks. Further, Energy Dispersive X-ray (EDAX) analysis revealed the variation in Te/Bi ratio with respect to autoclave temperature. Field emission scanning electron Microscope (FESEM) and the high resolution transmission electron Microscope (HRTEM) studies show the complete growth of hexagonal nanoplatelets at 200°C. Confocal Micro-Raman measurements revealed the occurrence of symmetry breaking in the synthesized hexagonal nanoplatelets. The electrical conductivity and the activation energy were recorded as 6.01×10−3S/m and 0.042eV respectively. Highest maximum absolute value of Seebeck coefficient of –355μV/K was obtained for the hexagonal nanoplatelets.

Thermoelectric properties of Graphene/Mn 0.7 Zn 0.3 Fe 2 O 4 composites

Abstract The Graphene/Mn0.7Zn0.3Fe2O4 composites were synthesized by coprecipitation and sintered by a spark-plasma-sintering (SPS) method. The thermoelectric properties of the sintered composites were evaluated in the temperature range of 343–973 K. The effect of graphene on the thermoelectrical properties of Mn0.7Zn0.3Fe2O4 was investigated. The dispersion of 2 wt% graphene in Mn0.7Zn0.3Fe2O4 effectively enhanced the electrical conductivity and the absolute value of Seebeck coefficient, while thermal conductivity was decreased. The results showed that the maximum ZT value of 0.035 at 973 K was obtained in the composite with 2 wt% graphene.

Preparation and thermoelectric properties of Bi2SexTe3−x bulk materials

Bi2Te3 and Bi2Se3 nanoplates were synthesized by a microwave-assisted wet chemical method, and Bi2SexTe3−x (x=1, 2, 3) bulk nanocomposites were then prepared by hot pressing the Bi2Te3 and Bi2Se3 nanoplates at 80MPa and 723K in vacuum. The phase composition and microstructures of the bulk samples were characterized by powder X-ray diffraction and field-emission scanning electron microscopy, respectively. The electrical conductivity of the Bi2SexTe3−x bulk nanocomposites increases with increasing Se content, and the Seebeck coefficient value is negative, showing n-type conduction. The absolute Seebeck coefficient value decreases with increasing Se content. A highest power factor, 24.5µWcm−1K−2, is achieved from the sample of x=1 at 369K among the studied samples.

Thermoelectric Properties of a Single Crystalline Ag2Te Nanowire

Silver chalcogenides have received much attention in potential thermoelectric materials research because of high carrier mobility and low effective mass. Among them, in Ag2Te, it was reported that the phase transition from monoclinic to cubic phase occurs at relatively low temperatures, so that extensive research for effective application using this material has been aroused. In this work, we investigated how 1-dimensional nanostructure affects the thermoelectric properties through as-synthesized single crystalline Ag2Te nanowires. Adopting well-defined thermoelectric MEMS device structure and transferring an individual Ag2Te nanowire, we measure electrical resistance and Seebeck coefficient as a function of temperature. When the phase changes from monoclinic to cubic, the resistance increases, while absolute Seebeck coefficient value decreases. These results are compared with previous reports for Ag2Te bulk and film, suggesting the increased density of states of the carriers due to nanowire structure.

First-Principles Simulation on Thermoelectric Properties in Low-Dimensional Materials

Thermoelectric properties were simulated for low-dimensional atomistic model structures based on first-principles calculation. New methodology about the first-principles simulation on Seebeck coefficient at arbitrary temperature and carrier concentration is presented. Dependence of Seebeck coefficient on scale, temperature, and carrier concentration has been demonstrated for silicon and beta silicon carbide nanowire models. Compared with the corresponding bulk models, a significant increase of the absolute value of Seebeck coefficient can be observed owing to quantum confinement by dimensional reduction. By the simulation with considering the energy dependence of the relaxation time, the Seebeck coefficient from the viewpoint of first principles can be evaluated as a range determined by the scattering constants peculiar to particular scattering processes.