Maximum Seebeck Coefficient Research Articles

Spin Seebeck effect in the 2D ferromagnetic CrPbTe3

Spin Seebeck effect has been mostly explored in bulk magnetic materials, but the efficiency is not large enough for device application. Recently, we have found that the 2D ferromagnetic CrPbTe3 layer has rather a high Curie temperature of 110 K. Thus, we have investigated the spin dependent Seebeck effect using the Boltzmann transport approach. We have found the largest carrier mobility and relaxation time in the minority spin electron carrier system due to the spin dependent effective mass and deformation potential constant. The onset energy of the electrical conductivity shows spin and carrier type dependency. Thus, both effective spin and effective charge Seebeck coefficients are originated from the majority spin carrier in the hole doped system whereas the minority spin carrier controls the effective spin and effective charge Seebeck coefficient in the electron doped system. We have obtained the maximum spin Seebeck coefficient of 1320 μV/K at 50 K. This value is suppressed at 100 K, but we still find a large spin Seebeck coefficient of 715 μV/K.

Pure V2O5 high-electricity transmission properties at low temperatures by structural changes

There have been many studies concentrating on high-temperature thermoelectric properties of non-doping V2O5 thin films and doping ones, but high power factor (PF) of V2O5 thermoelectrics have been rarely reported up to now, particularly low temperature ones. In this work, the thermoelectric performance of pure V2O5 at low temperature is reported where V2O5 commercial powders are successfully prepared into sintered blocks by spark plasma sintering (SPS) and annealing steps. It is clear that the annealing temperature plays a major role on the electrical transport properties due to the microstructure changes. At annealing temperature (623 K), the maximum Seebeck coefficient (205 K) and PFmax (186 K) arrive at −618 μV/K and 2.17 × 10−4 W/K2m, respectively, based on growth of grains, the reduction of grain boundaries and defect concentration. The PF is 2 orders of magnitude higher than the annealed of V2O5 film reported so far (Adv Mater Technol 2016;1:1600077). This research may provide an alternative strategy for the preparation of high-performance V2O5 thermoelectric devices.

Composition dependence of spin Seebeck voltage in YIG/Pt100−XRuX, Pt100−XCuX, and Pt100−X(Cu0.5Ru0.5)X

We investigated the composition effect on spin Seebeck coefficient in YIG/Pt100−XRuX, YIG/Pt100−XCuX, and YIG/Pt100−X(Cu0.5Ru0.5)X systems. In all systems the composition of around 50 (at%) showed the maximum spin Seebeck coefficient, which is considered as the result from the extrinsic spin Hall effect improvement since the resistivity was also increased with doping Ru and Cu into Pt host. In terms of the spin Seebeck coefficient dependence on doped element, YIG/Pt100−XCuX was the largest, followed in order by YIG/Pt100−X(Cu0.5Ru0.5)X, and YIG/Pt100−XRuX, although both of Cu and Ru have equally small spin Hall angle in the single state. The X-ray diffraction analysis showed that Cu doping most widely decreased the unit cell size of alloy, and consequently increased the resistivity. It is considered as a reason of improvement of the extrinsic spin Hall angle and the spin Seebeck voltage.

Improved Thermoelectric Performance in TiO2 Incorporated Polyaniline: A Polymer-Based Hybrid Material for Thermoelectric Generators

Enhanced thermoelectric performances have been achieved in hybrid nanocomposites of TiO2 incorporated into electrically conductive polyaniline (PANI) through a chemical polymerization process, for next-generation energy sources. Different weight percentages of TiO2 were used in hybrid nanocomposites and their charge transport properties were studied to understand the consequence of TiO2 incorporation in the PANI matrix. Aniline was used as reactant, and ammonium peroxydisulfate as polymerizing agent during synthesis process. The hybrid composites of TiO2 incorporated PANI were studied by using X-ray diffraction pattern, Fourier transform-infrared spectra and scanning electron microscopic images. The thermoelectric characteristics of this PANI-based composite were much improved as compared to pure PANI. The ordered chain structures of PANI, and the decrease of carrier hopping barrier with incorporation of TiO2 nanoparticles in the PANI chain matrix improved the charge carrier conduction and lead towards enhanced thermoelectric properties of these materials. The maximum Seebeck coefficient (S) as recorded 1.767 mV/°C, was fivefold larger as compared with pure PANI. The analysis of results reveal that these hybrid composites are potential candidates for next-generation thermoelectric generators with their light weight, environmentally friendly nature and cost-effectiveness for energy harvesting applications.

Anisotropic electronic transport properties of Ag-oped Mg3Sb2 crystal prepared by directional solidification

Ag-doped Mg3Sb2 crystals are successfully grown via a directional solidification method with high temperature gradient. The microstructure of the crystal is homogeneous and without precipitation. Both electrical conductivity and Seebeck coefficient are anisotropic in two crystallographic directions ([001] and [101]) due to anisotropic effective mass and mobility of the carriers. Thermal conductivity is isotropic too, and the maximum Seebeck coefficient is 265 μV K−1 in the [001] orientation, which represents a substantial improvement over previous results. As a consequence, the maximum power factor for the 2.5 at. % Ag-doped crystal is 1.21 mW m−1 K−2 in the [001] orientation, which results in an elevated ZT of 0.67 at T = 800 K. First principles calculations and Hall measurements are used to verify the experimental results.

Charge carrier density, mobility, and Seebeck coefficient of melt-grown bulk ZnGa2O4 single crystals

The temperature dependence of the charge carrier density, mobility, and Seebeck coefficient of melt-grown, bulk ZnGa2O4 single crystals was measured between 10 K and 310 K. The electrical conductivity at room temperature is about σ = 286 S/cm due to a high electron concentration of n = 3.26 × 1019 cm−3 caused by unintentional doping. The mobility at room temperature is μ = 55 cm2/V s, whereas the scattering on ionized impurities limits the mobility to μ = 62 cm2/Vs for temperatures lower than 180 K. The Seebeck coefficient relative to aluminum at room temperature is SZnGa2O4−Al=(−125±2) μV/K and shows a temperature dependence as expected for degenerate semiconductors. At low temperatures, around 60 K, we observed the maximum Seebeck coefficient due to the phonon drag effect.

Effect of transient low-grade solar heat on liquid thermogalvanic cells

Thermogalvanic cells have attracted huge attention for the conversion of low-grade waste heat into electricity due to their cost effectiveness. The environment in itself is a rich source of untapped energy such as energy from the sun, geothermal waste heat etc. However, the transient nature of this waste heat makes it a challenge for all-day electricity generation. This paper therefore seeks to investigate the effect of the transient nature of the ultra-low-grade solar energy on liquid thermogalvanic cell. Copper sulphate (CuSO4) electrolyte and copper electrodes were used. The electrolytes were contained in two pyrex 100-ml glass beaker with corks holding the electrode and a thermocouple in each beaker. A 42 cm long tube containing same electrolyte connected the two as a salt bridge. The electrolyte concentrations were varied from 0.2 to 1.0 M at a temperature difference ranging from 2 to 10 °C. The maximum Seebeck coefficient of 0.698 mV/K was recorded at a concentration of 0.8 M CuSO4 during heating and 0.798 mV/K at a concentration of 1.0 M during cooling. A maximum power output of 3.99 nWcm−2 was obtained at a concentration of 0.8 M.

Lower temperature of the structural transition, and thermoelectric properties in Sn-substituted GeTe

GeTe is a potential thermoelectric material for mid-temperature range applications. Here, we report on GeTe and Ge0.9Sn0.1Te prepared using a fast and simple arc-melting method. Their crystal structures have been analyzed by synchrotron X-ray diffraction. Calorimetry identified a shift in the rhombohedral to cubic structural transition temperature from 700 K to 557 K due to Sn alloying. Nevertheless, the temperature of the maximum Seebeck-coefficient is preserved, at 770 K. The thermoelectric properties are also reported, with a strong decrease of electric and thermal conductivities of the Sn-doped compound, as compared to the undoped one. The Hall-mobility also decreases strongly upon doping.

Enhanced Electrical Transport Properties via Defect Control for Screen-Printed Bi2Te3 Films over a Wide Temperature Range.

The application of screen-printed thin-film thermoelectric (TE) devices is still in its infancy, mainly due to low TE performance of screen-printed films and especially the poor electrical transport properties. Herein, we design and prepare a high-performance screen-printed Bi2Te3 film through introducing excessive Te-based nanosolder (Te-NS) to simultaneously realize the conduction channel construction and defect control. On one hand, the promoted carrier migration makes the electrical conductivity dramatically rise about 7 times, with a maximum power factor of 4.65 μW cm -1 K -2. Meanwhile, the defect formation mechanism in the screen-printed Bi2Te3 film after the introduction of Te-NS is also in-depth studied, and the bipolar conduction is reduced by increased generation of TeBi• and/or more suppression of BiTe', resulting in a postponed temperature of the maximum Seebeck coefficient. Hence, the large engineering power factor is achieved with excellent temperature linearity, indicating a possibility of screen-printed film application in a large temperature region. A TE device with a single leg has been fabricated to further demonstrate the generation validity. An open-circuit voltage of 11.34 mV and a maximum output power of 27.1 μW at a temperature gradient of 105 K have been achieved over a wide temperature range from 303 to 478 K. This study provides a theoretical and practical basis for the performance improvement of screen-printed TE films and devices.

Growth of SnSe single crystal via vertical vapor deposition method and characterization of its thermoelectric performance

In this work, a vertical vapor deposition method was developed to grow SnSe single crystals. More than thirty single crystal particles were simultaneously obtained and the largest size could up to 15 × 15 × 10 mm3. The as-grown crystal is tested has nearly Sn: Se = 1: 1 stoichiometric ratio and demonstrates standard orthorhombic Pnma space group at room temperature. Electrical transport measurement shows the present SnSe single crystal has a largest electrical conductivity σ = 39.6 S cm−1 near Pnma- Cmcm phase transition temperature, and the maximum Seebeck coefficient S = 566 μVK-1 is taken place around 580 K. Thermal transport analysis implies SnSe single crystal exhibits a lowest total thermal conductivity ktot=0.44 Wm−1 K−1 near Pnma- Cmcm phase transition. Finally, it is calculated the figure of merit ZT has a largest value ∼1.0 around 800 K that implies SnSe single crystal is a promising middle- temperature TE material.

Enhanced thermoelectric performance of SWNT/organic small molecule (OSM) hybrid materials by tuning of the energy level of OSMs

The SWNT/dmBT hybrid with a low barrier of 0.06 eV between SWNT and dmBT showed a maximum Seebeck coefficient of 78.5 μV K−1 and a power factor of 183.9 μW m−1 K−1, 1.5 and 4.6 times higher compared to the SWNT/dCNBT with a high barrier of 0.64 eV.

Thermoelectric performance of (GeTe)1−x(Sb2Te3)x fabricated by high pressure sintering method

(GeTe)1−x(Sb2Te3)x is one of good middle temperature thermoelectric materials. Here, the effects of x values and heat treatment (673 K 24 h) on the thermoelectric property of (GeTe)1−x(Sb2Te3)x (x = 0, 0.02, 0.04, 0.06) prepared by solid-state synthesis (873 K) and high pressure sintering (6 GPa) method were studied, the composition, microstructure, and the thermoelectric properties in temperature range of 300–731 K were investigated. The results indicate that high pressure sintering (HPS) is beneficial to the dissolution of Sb2Te3 in GeTe and the acquisition of nanocrystalline (GeTe)1−x(Sb2Te3)x. Soluble Sb2Te3 can greatly change the crystal structure of GeTe, and results in the high pressure phase and different thermoelectric property in (GeTe)1−x(Sb2Te3)x (x ≠ 0). Heat treatment does not change the high pressure phase of (GeTe)1−x(Sb2Te3)x (x ≠ 0), meanwhile it increases the crystal grain size of (GeTe)1−x(Sb2Te3)x (x ≠ 0). Samples of x = 0.04 and x = 0.06 show the maximum Seebeck coefficient value at 724 K, and (GeTe)0.98(Sb2Te3)0.02 shows the highest power factor (PF = 3.70 μW/mmK2 at 724 K). The largest value of ZT = 0.56 at 724 K is obtained for (GeTe)0.94(Sb2Te3)0.06.

Effect of TiO2 additive on thermoelectric properties of SrTiO3

Strontium titanate ([Formula: see text] has the advantages of being non-toxic, environmentally friendly and high-temperature stable, and has potential application in waste heat power generation at medium and high temperature. To explore the impact of TiO2 on the thermoelectric properties of SrTiO3, we synthesized TiO2/La10Nbb10-STO composite powders by hydrothermal method using precursor solution of 10[Formula: see text]mol.% La and 10[Formula: see text]mol.% Nb co-doped STO (La10Nb10-STO) containing TiO2 nanopowders with different molar ratio. After cold pressing and sintering, composite bulk materials were obtained, and their microstructure and thermoelectric transport properties were analyzed. With the increasing TiO2, although the thermal conductivity of TiO2/La10Nb10-STO composite decreased and the Seebeck coefficient increased, the minimum thermal conductivity and the maximum Seebeck coefficient were 2.54[Formula: see text][Formula: see text][Formula: see text] and 215[Formula: see text][Formula: see text]V[Formula: see text][Formula: see text], respectively, at 1000[Formula: see text]K, but the power factor decreased at high temperature due to the apparent decrease of electrical conductivity, resulting in the ZT values being lower than that of La0Nb10-STO without TiO2 addition at high temperature. Significantly, the addition of TiO2 can improve the thermoelectric performance of strontium titanate at low temperature. This approach is expected to improve the ZT of SrTiO3-based thermoelectric material through additional controlling of electrical conductivity.

Structural, Electronic and Thermoelectric Properties of Pb1−xSnxTe Alloys

The structural, electronic and thermoelectric properties of Pb1−xSnxTe (x = 0, 0.25, 0.5, 0.75, 1) alloys are investigated using density functional theory and the semi-classical Boltzmann transport theory. Both PbTe and SnTe binary alloys exhibit a semiconducting behavior with narrow direct bandgaps of 0.114 eV and 0.107 eV, respectively, at the L high-symmetry point. However, the alloying of Sn over Pb in PbTe alloy shows diverse electronic properties from a zero bandgap to 0.0833 eV depending upon the Pb/Sn concentrations. The p-type of PbTe is found to have a maximum Seebeck coefficient of 343.14 μV/K at 300 K, whereas the n-type of SnTe shows a peak of 246.32 μV/K at 300 K. The p-type of PbTe and n-type of SnTe exhibit the highest power factors of 119.76 × 10−3 Wm−1 K−2 and 148.32 × 10−3 Wm−1 K−2, respectively, at 900 K among all Pb1−xSnxTe alloys. However, Pb0.5Sn0.5Te alloy also shows a reasonably significant Seebeck coefficient and power factor for both the p- and n-type dopings. The interesting thermoelectric properties of these Pb1−xSnxTe alloys show high potential towards high thermoelectric efficiency and device applications.

Ultra-low thermal conductivity via interfacial phonon scattering in PbTe hoppercubes/PbTeO3 microrods for thermoelectric applications

PbTe/PbTeO3 composites were synthesized via hydrothermal method. Sodium hydroxide (NaOH) was used to control the morphology and the formation of PbTe/PbTeO3 composites. The as-prepared samples were extensively studied using various techniques. In the absence of NaOH, PbTeO3 microrods were obtained. The addition of NaOH at varying concentration (7.5 and 12.5 mmol) considerably influenced the phase ratio of PbTe hoppercubes and PbTeO3 microrods. The morphology dependent thermoelectric properties of PbTe/PbTeO3 composites were investigated in the temperature range of 300–660 K by using Spark Plasma Sintered pellet. It revealed that the lower concentration of NaOH (7.5 mmol), which contains the equivalent amount of PbTe hoppercubes and PbTeO3 microrods shows the maximum Seebeck coefficient of 438 μV/K at 420 K and minimum thermal conductivity of 0.44 W/mK at 660 K. Whereas, at higher concentration of NaOH (12.5 mmol) which contains more amount of PbTe hoppercubes and less PbTeO3 microrods shows the maximum Seebeck coefficient of 427 μV/K at 380 K and exhibited ultra-low thermal conductivity about 0.31 W/mK at 620 K. It clearly shows that the more amount of hoppercubes which contains less microrods scattered the phonons more at the grains boundaries of PbTe hoppercubes and PbTeO3 microrods. The possible phonon scattering mechanism of PbTe/PbTeO3 composites was proposed.

High thermoelectric power factor in SnSe2 thin film grown on Al2O3 substrate

Thermoelectric figure of merit (ZT) is highly sensitive to the carrier concentration and maximizes within the narrow region of 1019–1020 cm−3. The SnSe2 single crystal is predicted to have a high ZT value with carrier concentration in the range of 1019–1020 cm−3. Here, we grew SnSe2 thin film on Al2O3 substrate by pulsed laser deposition (PLD) with post-annealing at 400 °C in Argon for 60 min. The annealed thin film shows a high thermoelectric power factor up to 8 μW cm−1 K−2 at 220 K with a carrier concentration of 5.2 × 1019 cm−3. A hexagonal crystal structure of the SnSe2 thin film was confirmed by X-ray diffraction and Raman spectra measurements. The thin film showed an n-type semiconductor behavior. Maximum electrical conductivity and Seebeck coefficient were obtained at 220 K with the values of 210 Scm−1 and −192 μVK−1, respectively.

Vanadium salt assisted solvothermal reduction of graphene oxide and the thermoelectric characterisation of the reduced graphene oxide in bulk and as composite

Abstract The solvothermal reduction of graphene oxide (GO), modified by the addition of vanadium chloride, resulted in an increased reduction degree of the reduced graphene oxide (rGO), which is reflected by a remarkably increased electrically conductivity of up to 8.5 S/cm, a value 30 times higher than that of rGO prepared without vanadium salt addition. Parallel with this increase, the thermoelectrical properties of rGO are improved, with a reached maximum Seebeck coefficient of 13.7 μV/K. The rGOs were used as fillers in flexible styrene-butadiene-styrene triblock copolymer composites prepared by solution mixing. Compared to the traditionally prepared reduced graphene oxide, the new product provides up to 60 times higher conductivity to the composite, while the Seebeck coefficient is nearly the same. The highest power factor of 4.6 × 10−4 μW/(m∙K2) was achieved at 100 °C with 30 wt% loading, which is 30 times higher than that of the traditional reduced graphene oxide containing composite.

Microstructure and thermoelectric performance of n-type Co4Sb11.3Te0.5Se0.2 skutterudite synthesized via microwave heating

The Te-/Se-doped n-type Co4Sb11.3Te0.5Se0.2 skutterudite thermoelectric bulk was successfully fabricated by the combination of microwave synthesis and spark plasma sintering technique. The microstructure and the electrical and thermal transport properties have been systematically investigated. The experimental results show that nearly single-phase skutterudites grow in merely 5 min microwave heating. The average matrix grain size of Co4Sb11.3Te0.5Se0.2 is ∼2 μm. The carrier concentration and mobility of Co4Sb11.3Te0.5Se0.2 are 1.943×1020 n/cm-3 and 23.17 cm2V-1s-1, respectively. The maximum Seebeck coefficient is -204 μVK-1. The lattice and total thermal conductivity from room temperature to 773K are 2.11∼3.32 and 2.88∼3.78 Wm-1K-1, respectively. The highest ZT of 0.59 of Co4Sb11.3Te0.5Se0.2 was achieved at 673 K. The present synthetic method is superior especially in term of the synthesis efficiency.

Detecting the major charge-carrier scattering mechanism in graphene antidot lattices

Charge carrier scattering is critical to the electrical properties of two-dimensional materials such as graphene, black phosphorene, and tellurene. Beyond pristine two-dimensional materials, further tailored properties can be achieved by nanoporous patterns such as nano- or atomic-scale pores (antidots) across the material. As one example, structure-dependent electrical/optical properties for graphene antidot lattices (GALs) have been studied in recent years. However, detailed charge carrier scattering mechanism is still not fully understood. In this paper, the energy sensitivity of charge-carrier scattering and thus the dominant scattering mechanisms are revealed for GALs by analyzing the maximum Seebeck coefficient with a tuned gate voltage and thus shifted Fermi levels. It shows that the scattering from pore-edge-trapped charges is dominant. For thermoelectric interests, the gate-voltage-dependent power factor for a GAL with the square pattern can reach as high as 554 μW/cm⋅K2 at 400 K. With their high thermal conductivities and power factors, these GALs can be well suitable for “active coolers” within electronic devices, where heat generated at the hot spot can be removed with both passive heat conduction and active Peltier cooling.

Enhanced Thermoelectric Properties for PEDOT:PSS/Undoped Ge Thin‐Film Bilayered Heterostructures

AbstractModulation doping is one of the strategies to improve thermoelectric power factors of nanocomposites and thin‐film bilayered heterostructures by effectively increasing electrical conductivity. Here, it is reported that thin‐film heterostructures of heavily doped p‐type organic conducting polymer, poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and undoped thin‐film Ge can enhance thermoelectric power factor by modulation doping. The maximum power factor and Seebeck coefficient of the bilayered heterostructures are 154 µW m−1 K−2 and 398 µV K−1, respectively, corresponding to 47‐fold and 41‐fold increases compared to those of bulk PEDOT:PSS and 64‐fold increase compared to power factor of undoped Ge. The enhancements in power factor and Seebeck coefficient are quantitatively described by the hole transfer from PEDOT:PSS to Ge, which takes into account the band alignment at the interface detected by Kraut's method. Agreement between the simulation and experiment results also implies predictability of thermoelectric performances of nanoscale bilayered heterostructures in general, when band offset, Fermi level, and individual electronic properties are available. This work can be further extended to predict performance of other nanoscale combinations of thermoelectric and other electronic materials in general.