Showing papers on "Seebeck coefficient published in 2012"
TL;DR: The research suggests that striving to achieve band degeneracy by means of compositional variations is an effective strategy for enhancing the thermoelectric properties of these materials.
Abstract: Mg(2)Si and Mg(2)Sn are indirect band gap semiconductors with two low-lying conduction bands (the lower mass and higher mass bands) that have their respective band edges reversed in the two compounds. Consequently, for some composition x, Mg(2)Si(1-x)Sn(x) solid solutions must display a convergence in energy of the two conduction bands. Since Mg(2)Si(1-x)Sn(x) solid solutions are among the most prospective of the novel thermoelectric materials, we aim on exploring the influence of such a band convergence (valley degeneracy) on the Seebeck coefficient and thermoelectric properties in a series of Mg(2)Si(1-x)Sn(x) solid solutions uniformly doped with Sb. Transport measurements carried out from 4 to 800 K reveal a progressively increasing Seebeck coefficient that peaks at x=0.7. At this concentration the thermoelectric figure of merit ZT reaches exceptionally large values of 1.3 near 700 K. Our first principles calculations confirm that at the Sn content x≈0.7 the two conduction bands coincide in energy. We explain the high Seebeck coefficient and ZT values as originating from an enhanced density-of-states effective mass brought about by the increased valley degeneracy as the two conduction bands cross over. We corroborate the increase in the density-of-states effective mass by measurements of the low temperature specific heat. The research suggests that striving to achieve band degeneracy by means of compositional variations is an effective strategy for enhancing the thermoelectric properties of these materials.
1,044 citations
TL;DR: In this paper, the effect of electronic density of states (DOS) distortions on the thermopower of thermoelectric semiconductors has been investigated and the authors have discussed the conditions for DOS distortions to increase the thermopelectric power of the semiconductor.
Abstract: Distortions of the electronic density of states (DOS) are a potent mechanism to increase the thermopower of thermoelectric semiconductors, thereby increasing their power factor. We review band-structure engineering approaches that have been used to achieve this, resonant impurity levels, dilute Kondo effects, and hybridization effects in strongly correlated electron systems. These can increase the thermoelectric power of metals and semiconductors through two mechanisms: (1) the added density of states increases the thermopower in a nearly temperature-independent way; (2) resonant scattering results in a strong electron energy filtering effect that increases the thermopower at cryogenic temperatures where the electron–phonon interactions are weaker. Electronic structure calculation results for Tl:PbTe and Ti:PbTe are contrasted and identify the origin of the thermopower enhancement in Tl:PbTe. This leads to a discussion of the conditions for DOS distortions to produce thermopower enhancements and illustrates the existence of an optimal degree of delocalization of the impurity states. The experimentally observed resonant levels in several III–V, II–VI, IV–VI and V2-VI3 compound semiconductor systems are reviewed.
740 citations
TL;DR: In this paper, the thermoelectric properties of promising oxide materials are reviewed and approaches for improving performance through doping are discussed, and different types of oxides used for thermocyanide applications are compared.
Abstract: Thermoelectric energy conversion can be used to capture electric power from waste heat in a variety of applications. The materials that have been shown to have the best thermoelectric properties are compounds containing elements such as tellurium and antimony. These compounds can be oxidized if exposed to the high temperature air that may be present in heat recovery applications. Oxide materials have better stability in oxidizing environments, so their use enables the fabrication of more durable devices. Thus, although the thermoelectric properties of oxides are inferior to those of the compounds mentioned above, their superior stability may expand potential the high temperature application of thermoelectric energy conversion. In this paper, the thermoelectric properties of promising oxide materials are reviewed. The different types of oxides used for thermoelectric applications are compared and approaches for improving performance through doping are discussed.
474 citations
TL;DR: In this paper, the authors demonstrate that the benefit of light effective mass contributes to high zT in n-type thermoelectric PbTe, where doping and temperature can be used to tune the effective mass.
Abstract: High Seebeck coefficient by creating large density-of-states effective mass through either electronic structure modification or manipulating nanostructures is commonly considered as a route to advanced thermoelectrics However, large density-of-state due to flat bands leads to large transport effective mass, which results in a simultaneous decrease of mobility In fact, the net effect of such a high effective mass is a lower thermoelectric figure of merit, zT, when the carriers are predominantly scattered by phonons according to the deformation potential theory of Bardeen–Shockley We demonstrate that the beneficial effect of light effective mass contributes to high zT in n-type thermoelectric PbTe, where doping and temperature can be used to tune the effective mass This clear demonstration of the deformation potential theory to thermoelectrics shows that the guiding principle for band structure engineering should be low effective mass along the transport direction
470 citations
TL;DR: The theoretical basis for understanding the spin Seebeck effect is presented and the inverse spin Hall effect converts the injected spin current into a transverse charge voltage, thereby producing electromotive force as in the conventional charge Seebeck device.
Abstract: The spin Seebeck effect refers to the generation of a spin voltage caused by a temperature gradient in a ferromagnet, which enables the thermal injection of spin currents from the ferromagnet into an attached nonmagnetic metal over a macroscopic scale of several millimeters. The inverse spin Hall effect converts the injected spin current into a transverse charge voltage, thereby producing electromotive force as in the conventional charge Seebeck device. Recent theoretical and experimental efforts have shown that the magnon and phonon degrees of freedom play crucial roles in the spin Seebeck effect. In this article, we present the theoretical basis for understanding the spin Seebeck effect and briefly discuss other thermal spin effects.
398 citations
TL;DR: In this paper, the energy-filtering effect was successfully employed at the organic-inorganic semiconductor interface of poly(3-hexylthiophene) (P3HT) nanocomposites with the addition of Bi2Te3 nanowires, where low-energy carriers were strongly scattered by the appropriately engineered potential barrier of the P3HT-Bi 2Te3 interface.
Abstract: The energy-filtering effect was successfully employed at the organic–inorganic semiconductor interface of poly(3-hexylthiophene) (P3HT) nanocomposites with the addition of Bi2Te3 nanowires, where low-energy carriers were strongly scattered by the appropriately engineered potential barrier of the P3HT–Bi2Te3 interface. The resulting P3HT–Bi2Te3 nanocomposites exhibited a high power factor of 13.6 μW K−2 m−1 compared to that of 3.9 μW K−2 m−1 in P3HT. The transport characteristics of nanocomposites, including the carrier concentration, mobility, and energy-dependent scattering parameter, were revealed by the experimental measurements of electrical conductivity, Seebeck coefficient, and Hall coefficient to quantitatively elucidate the carrier energy scattering at the P3HT–Bi2Te3 interface. The ability to rationally engineer the organic–inorganic semiconductor interfaces of polymer nanocomposites to achieve an improved Seebeck coefficient and power factor provides a potential route to high-performance, large-area, and flexible polymer thermoelectric materials.
350 citations
TL;DR: By adding aluminium (Al) into lead selenide (PbSe), the authors successfully prepared n-type PbSe thermoelectric materials with a figure-of-merit (ZT) of 1.3 at 850 K.
Abstract: By adding aluminium (Al) into lead selenide (PbSe), we successfully prepared n-type PbSe thermoelectric materials with a figure-of-merit (ZT) of 1.3 at 850 K. Such a high ZT is achieved by a combination of high Seebeck coefficient caused by very possibly the resonant states in the conduction band created by Al dopant and low thermal conductivity from nanosized phonon scattering centers.
345 citations
TL;DR: The enhanced thermoelectric properties of selenium (Se) doped bismuth telluride (Bi(2)Te(3-x)Se(x)) nanoplatelet (NP) composites synthesized by the polyol method are reported on.
Abstract: We report on the enhanced thermoelectric properties of selenium (Se) doped bismuth telluride (Bi2Te3–xSex) nanoplatelet (NP) composites synthesized by the polyol method. Variation of the Se composition within NPs is demonstrated by X-ray diffraction and Raman spectroscopy. While the calculated lattice parameters closely follow the Vegard’s law, a discontinuity in the shifting of the high frequency (Eg2 and A1g2) phonon modes illustrates a two mode behavior for Bi2Te3–xSex NPs. The electrical resistivity (ρ) of spark plasma sintered pellet composites shows metallic conduction for pure Bi2Te3 NP composites and semiconducting behavior for intermediate Se compositions. The thermal conductivity (κ) for all NP composites is much smaller than the bulk values and is dominated by microstructural grain boundary scattering. With temperature dependent electrical and thermal transport measurements, we show that both the thermoelectric power S (−259 μV/K) and the figure of merit ZT (0.54) are enhanced by nearly a facto...
333 citations
TL;DR: Since these fabrics have the potential to be cheaper, lighter, and more easily processed than the commonly used thermoelectric bismuth telluride, the overall performance of the fabric shows promise as a realistic alternative in a number of applications such as portable lightweight electronics.
Abstract: Thermoelectrics are materials capable of the solid-state conversion between thermal and electrical energy. Carbon nanotube/polymer composite thin films are known to exhibit thermoelectric effects, however, have a low figure of merit (ZT) of 0.02. In this work, we demonstrate individual composite films of multiwalled carbon nanotubes (MWNT)/polyvinylidene fluoride (PVDF) that are layered into multiple element modules that resemble a felt fabric. The thermoelectric voltage generated by these fabrics is the sum of contributions from each layer, resulting in increased power output. Since these fabrics have the potential to be cheaper, lighter, and more easily processed than the commonly used thermoelectric bismuth telluride, the overall performance of the fabric shows promise as a realistic alternative in a number of applications such as portable lightweight electronics.
320 citations
TL;DR: The first concurrent determination of conductance (G) and thermopower (S) of single-molecule junctions via direct measurement of electrical and thermoelectric currents using a scanning tunneling microscope-based break-junction technique was reported in this paper.
Abstract: We report the first concurrent determination of conductance (G) and thermopower (S) of single-molecule junctions via direct measurement of electrical and thermoelectric currents using a scanning tunneling microscope-based break-junction technique. We explore several amine-Au and pyridine-Au linked molecules that are predicted to conduct through either the highest occupied molecular orbital (HOMO) or the lowest unoccupied molecular orbital (LUMO), respectively. We find that the Seebeck coefficient is negative for pyridine-Au linked LUMO-conducting junctions and positive for amine-Au linked HOMO-conducting junctions. Within the accessible temperature gradients (<30 K), we do not observe a strong dependence of the junction Seebeck coefficient on temperature. From histograms of thousands of junctions, we use the most probable Seebeck coefficient to determine a power factor, GS(2), for each junction studied, and find that GS(2) increases with G. Finally, we find that conductance and Seebeck coefficient values are in good quantitative agreement with our self-energy corrected density functional theory calculations.
249 citations
TL;DR: In this article, carbon nanotubes were doped with both polyethyleneimine (PEI) and sodium borohydride (NaBH4), showing excellent n-type characteristics with thermopower values as large as −80 μV K−1.
Abstract: This report demonstrates an exciting new paradigm for thermoelectric energy conversion with both n- and p-type organic materials that possess mechanical flexibility, simple fabrication processes, and stability in air. In order to synthesize n-type samples with membranes and papers, carbon nanotubes were doped with both polyethyleneimine (PEI) and sodium borohydride (NaBH4), showing excellent n-type characteristics with thermopower values as large as −80 μV K−1. Thermoelectric modules made of both n- and p-type composites were fabricated to demonstrate thermoelectric voltage and power generation with one, two, and three p–n couples connected in series. The testing modules produced ∼6 mV thermoelectric voltage, with ∼25 nW generated power upon application of ∼22 °C temperature gradients. These promising results show that further work with many junctions connected in series would result in scalable organic p–n couple modules, which can generate power from temperature gradients or provide cooling for various electronic devices.
TL;DR: In this article, high phase-purity BiCuSeO polycrystalline materials with fine grains were synthesized by a facile method combining a solid-state reaction and spark plasma sintering.
Abstract: This work revealed that BiCuSeO oxyselenide is a potential oxide-based thermoelectric material, whose dimensionless figure of merit (ZT) reaches ∼0.70 at 773 K. High phase-purity BiCuSeO polycrystalline materials with fine grains were synthesized by a facile method combining a solid-state reaction and spark plasma sintering. Purifying the constitutive phase and reducing the grain sizes by introducing a high-energy ball milling process before spark plasma sintering were found to be effective in property enhancement. The resultant single-phased BiCuSeO sample derived from ball-milled powders shows good electrical conductivity above 4.0 × 103 S m−1 and a large Seebeck coefficient above 200 μV K−1. This compound has a low thermal conductivity (∼0.5 W m−1 K−1), which is associated with its low phonon transport speed and Young's modulus. Results indicated that BiCuSeO-based materials are promising for energy conversion applications in the moderate temperature range.
TL;DR: In this paper, the authors investigate the characteristics that distinguish the resonant state mechanism from that due to multiple valence bands and their effect on the thermoelectric figure of merit, zT.
Abstract: The Seebeck coefficient of p-type PbTe can be enhanced at 300 K, either due to the addition of Tl-resonant states or by manipulation of the multiple valence bands by alloying with isovalent compounds, such as MgTe. PbTe alloyed with MnTe shows a similar thermopower enhancement that could be due to either mechanism. Here we investigate the characteristics that distinguish the resonant state mechanism from that due to multiple valence bands and their effect on the thermoelectric figure of merit, zT. Ultimately, we find that the transport properties of PbTe alloyed with MnTe can be explained by alloy scattering and multiple band model that result in a zT as high as 1.6 at 700 K, and additionally a ~30% enhancement of the average zT.
TL;DR: In this paper, the authors studied the electrical and thermal transport properties of lead-based chalcogenides (PbTe, PbSe, and PbS) with special emphasis on the lattice and the bipolar thermal conductivity.
TL;DR: In this paper, a flexible thermoelectric nanogenerator (TENG) was developed based on a Te-nanowire/poly(3-hexyl thiophene) (P3HT) polymer composite material with a positive Seebeck coefficient of 285 μV/K.
Abstract: We have developed a flexible thermoelectric nanogenerator (TENG) that is based on a Te-nanowire/poly(3-hexyl thiophene) (P3HT) polymer composite as the thermoelectric material with a positive Seebeck coefficient of 285 μV/K. A linear relationship between the output voltage of TENG and the temperature difference across the device was observed. Under a temperature difference of 55 K, two TENGs can provide an output voltage of 38 mV in serial connection, or a current density exceeding 32 nA/mm2 in parallel connection. We demonstrated that the flexible TENG can be used as a wearable energy harvester by using human body temperature as the energy source. In addition, the TENG can also be used as a self-powered temperature sensor with a response time of 17 s and a reset time of 9 s. The detection sensitivity of the sensor can reach 0.15 K in ambient atmosphere.
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TL;DR: A thermoelectric nanogenerator made from a single Sb-doped ZnO micro/nanobelt that generates an output power of about 1.94 nW under a temperature difference of 30 K between the two electrodes is demonstrated.
Abstract: We demonstrate a thermoelectric nanogenerator (NG) made from a single Sb-doped ZnO micro/nanobelt that generates an output power of about 1.94 nW under a temperature difference of 30 K between the two electrodes. A single Sb-doped ZnO microbelt was bonded at its ends on a glass substrate as a NG, which can give an output voltage of 10 mV and an output current of 194 nA. The single Sb-doped ZnO microbelt shows a Seebeck coefficient of about −350 μV/K and a high power factor of about 3.2 × 10–4 W/mK2. The fabricated NG demonstrated its potential to work as a self-powered temperature sensor with a reset time of about 9 s.
TL;DR: In this article, a graphite oxide (GO)/ordered polyaniline (PANI) composites have been prepared through an in situ polymerization, where the PANI grew along the surface of exfoliated GO as a template to form a more ordered structure with high crystallinity during polymerization.
TL;DR: Electrical conductance and thermopower measurements on InAs nanowires synthesized by chemical vapor deposition are reported and the possibility to modulate semiconductor nanowire's thermoelectric properties through 1D subband formation in the diffusive transport regime for electron is experimentally shown.
Abstract: We report electrical conductance and thermopower measurements on InAs nanowires synthesized by chemical vapor deposition. Gate modulation of the thermopower of individual InAs nanowires with a diameter around 20 nm is obtained over T = 40–300 K. At low temperatures (T < ∼100 K), oscillations in the thermopower and power factor concomitant with the stepwise conductance increases are observed as the gate voltage shifts the chemical potential of electrons in InAs nanowire through quasi-one-dimensional (1D) subbands. This work experimentally shows the possibility to modulate semiconductor nanowire’s thermoelectric properties through 1D subband formation in the diffusive transport regime for electron, a long-sought goal in nanostructured thermoelectrics research. Moreover, we point out the scattering (or disorder) induced energy level broadening as the limiting factor in smearing out the 1D confinement enhanced thermoelectric power factor.
TL;DR: In this paper, the electrical transport properties of poly(3,4-ethylenedioxythiophen)/poly(4-styrene-sulfonate) (PEDOT:PSS) with PEDOT-to-PSS ratios from 1:1 to 1:30 were investigated.
Abstract: We have investigated the electrical transport properties of poly(3,4-ethylenedioxythiophen)/poly(4-styrene-sulfonate) (PEDOT:PSS) with PEDOT-to-PSS ratios from 1:1 to 1:30. By combining impedance spectroscopy with thermoelectric measurements, we are able to independently determine the variation of electrical conductivity and charge carrier density with PSS content. We find the charge carrier density to be independent of the PSS content. Using a generalized effective media theory, we show that the electrical conductivity in PEDOT:PSS can be understood as percolation between sites of highly conducting PEDOT:PSS complexes with a conductivity of 2.3 (Ωcm)−1 in a matrix of excess PSS with a low conductivity of 10−3 (Ω cm)−1. In addition to the transport properties, the thermoelectric power factors and Seebeck coefficients have been determined. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012
TL;DR: In this paper, the authors established a three-dimensional finite element model of thermoelectric module based on low-temperature thermocorlectric material bismuth telluride, and medium-temorperature thermoric material filled-skutterudite.
TL;DR: The semiconductor-superionic conductor phase transition is put forward for the first time as a new and effective way to selectively optimize the thermoelectric power factor based on the modulation of the electric transport property across the phase transition.
Abstract: Thermoelectric has long been recognized as a potentially transformative energy conversion technology due to its ability to convert heat directly into electricity. However, how to optimize the three interdependent thermoelectric parameters (i.e., electrical conductivity σ, Seebeck coefficient S, and thermal conductivity κ) for improving thermoelectric properties is still challenging. Here, we put forward for the first time the semiconductor–superionic conductor phase transition as a new and effective way to selectively optimize the thermoelectric power factor based on the modulation of the electric transport property across the phase transition. Ultra low value of thermal conductivity was successfully retained over the whole investigated temperature range through the reduction of grain size. As a result, taking monodisperse Ag2Se nanocrystals for an example, the maximized ZT value can be achieved around the temperature of phase transition. Furthermore, along with the effective scattering of short-wavelengt...
TL;DR: In this article, the authors investigated thermoelectric properties of synthesized mineral tetrahedrites, which have a cubic and complex crystal structure, and showed that the thermopower was increased and thermal conductivity was decreased through various substitutions.
Abstract: We have investigated thermoelectric properties of synthesized mineral Cu10Tr2Sb4S13 (Tr = Mn, Fe, Co, Ni, Cu, and Zn) tetrahedrites, which have a cubic and complex crystal structure. The mother phase Tr = Cu shows metal–semiconductor transition and anomalous hysteresis. Through various Tr substitutions, the thermopower was increased and thermal conductivity was decreased. Results show that Tr = Ni had the largest dimensionless figure of merit Z T of 0.15 at 340 K. The main advantage for the large Z T is the quite low lattice thermal conductivity. Because of the large Z T and the environmentally friendly components, tetrahedrites are anticipated as a good thermoelectric material.
TL;DR: In this paper, a double quantum dot system coupled to external magnetic/nonmagnetic leads is investigated theoretically, and the basic thermoelectric transport characteristics, like thermopower, electronic contribution to heat conductance, and corresponding figure of merit, have been calculated in terms of the linear response theory and Green function formalism in the Hartree-Fock approximation for Coulomb interactions.
Abstract: Thermoelectric effects in a double quantum dot system coupled to external magnetic/nonmagnetic leads are investigated theoretically. The basic thermoelectric transport characteristics, like thermopower, electronic contribution to heat conductance, and the corresponding figure of merit, have been calculated in terms of the linear response theory and Green function formalism in the Hartree-Fock approximation for Coulomb interactions. An enhancement of the thermal efficiency (figure of merit $ZT$) due to Coulomb blockade has been found. The magnitude of $ZT$ is further considerably enhanced by quantum interference effects. Both the Coulomb correlations and interference effects lead to strong violation of the Wiedemann-Franz law. The influence of spin-dependent transport and spin bias on the thermoelectric effects (especially on Seebeck and spin Seebeck effects) is also analyzed.
TL;DR: It is proposed that the giant spin Seebeck effect is mediated by phonon–electron drag, which changes the electrons’ momentum and directly modifies the spin-splitting energy through spin–orbit interactions.
Abstract: A giant spin Seebeck effect—three orders of magnitude greater than previously detected—has been observed in a non-magnetic material, InSb; the proposed mechanism relies only on phonon drag and spin–orbit interactions in a spin-polarized system, not on magnetic exchange. Heat cycles provide almost all of the energy that a modern civilization consumes. The thermoelectric cycle, a latecomer compared with steam and gases, generates electrical power through the Seebeck effect, whereby an electric voltage is generated when a conductor is placed in a temperature gradient. The 2008 discovery of the spin Seebeck effect (
go.nature.com/dlvhz2
) — whereby a thermal gradient applied to a spin-polarized material leads to a spatially varying transverse spin current in an adjacent non-spin-polarized material — led to a new line of research in spintronics. In this issue of Nature, Jaworski et al. describe something similar but three orders of magnitude more powerful, a 'giant spin Seebeck effect' in a material (indium antimonide, InSb) that is non-magnetic but that has strong spin–orbit coupling and phonon–electron drag. They propose a mechanism for this phenomenon that relies on spin polarization only, not on magnetic exchange. The results, say the authors, show that the spin Seebeck effect can be of a magnitude that may make spin-based thermal-energy converters a reality, and possibly competitive with existing technologies. The spin Seebeck effect is observed when a thermal gradient applied to a spin-polarized material leads to a spatially varying transverse spin current in an adjacent non-spin-polarized material, where it gets converted into a measurable voltage. It has been previously observed with a magnitude of microvolts per kelvin in magnetically ordered materials, ferromagnetic metals1, semiconductors2 and insulators3. Here we describe a signal in a non-magnetic semiconductor (InSb) that has the hallmarks of being produced by the spin Seebeck effect, but is three orders of magnitude larger (millivolts per kelvin). We refer to the phenomenon that produces it as the giant spin Seebeck effect. Quantizing magnetic fields spin-polarize conduction electrons in semiconductors by means of Zeeman splitting, which spin–orbit coupling amplifies by a factor of ∼25 in InSb. We propose that the giant spin Seebeck effect is mediated by phonon–electron drag, which changes the electrons’ momentum and directly modifies the spin-splitting energy through spin–orbit interactions. Owing to the simultaneously strong phonon–electron drag and spin–orbit coupling in InSb, the magnitude of the giant spin Seebeck voltage is comparable to the largest known classical thermopower values.
TL;DR: In this article, the authors reported on bulk nanostructured (NS) undoped Bi2Te3 prepared via a promising chemical synthetic route, which achieved a peak value of ∼1.1 at 340 K. The average grain size of the final compacts was obtained as 90 ± 5 nm as calculated from electron micrographs.
Abstract: Bismuth telluride (Bi2Te3) is the best-known commercially used thermoelectric material in the bulk form for cooling and power generation applications at ambient temperature. However, its dimensionless figure-of-merit-ZT around 1 limits the large-scale industrial applications. Recent studies indicate that nanostructuring can enhance ZT while keeping the material form of bulk by employing an advanced synthetic process accompanied with novel consolidation techniques. Here, we report on bulk nanostructured (NS) undoped Bi2Te3 prepared via a promising chemical synthetic route. Spark plasma sintering has been employed for compaction and sintering of Bi2Te3 nanopowders, resulting in very high densification (>97%) while preserving the nanostructure. The average grain size of the final compacts was obtained as 90 ± 5 nm as calculated from electron micrographs. Evaluation of transport properties showed enhanced Seebeck coefficient (−120 μV K−1) and electrical conductivity compared to the literature state-of-the-art (30% enhanced power factor), especially in the low temperature range. An improved ZT for NS bulk undoped Bi2Te3 is achieved with a peak value of ∼1.1 at 340 K.
TL;DR: This study highlights an optimized temperature range for the pelletization of the nanoplatelet composites for TE applications and provides a subtle understanding of the grain growth mechanism and the filtering of low energy electrons and phonons with thermoelectric interfaces.
Abstract: Control of competing parameters such as thermoelectric (TE) power and electrical and thermal conductivities is essential for the high performance of thermoelectric materials. Bulk-nanocomposite materials have shown a promising improvement in the TE performance due to poor thermal conductivity and charge carrier filtering by interfaces and grain boundaries. Consequently, it has become pressingly important to understand the formation mechanisms, stability of interfaces and grain boundaries along with subsequent effects on the physical properties. We report here the effects of the thermodynamic environment during spark plasma sintering (SPS) on the TE performance of bulk-nanocomposites of chemically synthesized Bi2Te2.7Se0.3 nanoplatelets. Four pellets of nanoplatelets powder synthesized in the same batch have been made by SPS at different temperatures of 230, 250, 280, and 350 °C. The X-ray diffraction, transmission electron microscopy, thermoelectric, and thermal transport measurements illustrate that the ...
TL;DR: In this article, a high yield and upscalable colloidal synthesis route for the production of quaternary I2−II−IV-VI4 nanocrystals, particularly stannite Cu2+xCd1−xSnSe4, with narrow size distribution and precisely controlled composition is presented.
Abstract: A high-yield and upscalable colloidal synthesis route for the production of quaternary I2–II–IV–VI4 nanocrystals, particularly stannite Cu2+xCd1–xSnSe4, with narrow size distribution and precisely controlled composition is presented. It is also shown here how the diversity of valences in the constituent elements allows an effective control of their electrical conductivity through the adjustment of the cation ratios. At the same time, while the crystallographic complexity of quaternary chalcogenides is associated with intrinsically low thermal conductivities, the reduction of the lattice dimensions to the nanoscale further reduces the materials thermal conductivity. In the specific case of the stannite crystal structure, a convenient slab distribution of the valence band maximum states permits a partial decoupling of the p-type electrical conductivity from both the Seebeck coefficient and the thermal conductivity. Combining these features, we demonstrate how an initial optimization of the nanocrystals Cd/C...
TL;DR: In this article, the thermoelectric properties of hybrid graphene/boron nitride nanoribbons (BCNNRs) were investigated using the nonequilibrium Green's function approach.
Abstract: The thermoelectric properties of hybrid graphene/boron nitride nanoribbons (BCNNRs) are investigated using the nonequilibrium Green’s function approach. We find that the thermoelectric figure of merit (ZT ) can be remarkably enhanced by periodically embedding hexagonal BN (h-BN) into graphene nanoribbons (GNRs). Compared to pristine GNRs, the ZT for armchair-edged BCNNRs with width index 3p + 2 is enhanced 10–20 times, while the ZT of nanoribbons with other widths is enhanced by just 1.5–3 times. As for zigzag-edge nanoribbons, the ZT is enhanced 2–3 times. This improvement comes from the combined increase in the Seebeck coefficient and the reduction in the thermal conductance outweighing the decrease in the electrical conductance. In addition, the effect of the component ratio of h-BN on the thermoelectric transport properties is discussed. These results qualify BCNNRs as a promising candidate for building outstanding thermoelectric devices.
TL;DR: In this article, a general, three-dimensional numerical model of thermoelectric devices with consideration of coupling of temperature field and electric potential field was developed to figure out the performance of TECs with the temperature dependent thermal conductivity, electric conductivity and Seebeck coefficient of semiconductor materials.
TL;DR: In this paper, a model is proposed, showing that randomly distributed potential barriers (such as those found in polycrystalline films) may lead to the simultaneous occurrence of energy filtering and carrier localization, which may also affect the thermoelectric properties of a material.