Showing papers on "Seebeck coefficient published in 2011"
TL;DR: It is demonstrated that it is possible to direct the convergence of many valleys in a bulk material by tuning the doping and composition, leading to an extraordinary zT value of 1.8 at about 850 kelvin.
Abstract: Thermoelectric generators, which directly convert heat into electricity, have long been relegated to use in space-based or other niche applications, but are now being actively considered for a variety of practical waste heat recovery systems—such as the conversion of car exhaust heat into electricity. Although these devices can be very reliable and compact, the thermoelectric materials themselves are relatively inefficient: to facilitate widespread application, it will be desirable to identify or develop materials that have an intensive thermoelectric materials figure of merit, zT, above 1.5 (ref. 1). Many different concepts have been used in the search for new materials with high thermoelectric efficiency, such as the use of nanostructuring to reduce phonon thermal conductivity, which has led to the investigation of a variety of complex material systems. In this vein, it is well known, that a high valley degeneracy (typically ≤6 for known thermoelectrics) in the electronic bands is conducive to high zT, and this in turn has stimulated attempts to engineer such degeneracy by adopting low-dimensional nanostructures. Here we demonstrate that it is possible to direct the convergence of many valleys in a bulk material by tuning the doping and composition. By this route, we achieve a convergence of at least 12 valleys in doped PbTe_(1) − _(x)Se_(x) alloys, leading to an extraordinary zT value of 1.8 at about 850 kelvin. Band engineering to converge the valence (or conduction) bands to achieve high valley degeneracy should be a general strategy in the search for and improvement of bulk thermoelectric materials, because it simultaneously leads to a high Seebeck coefficient and high electrical conductivity.
2,964 citations
TL;DR: In this paper, the authors review recent experimental and theoretical results on nanostructured materials of various dimensions: superlattices, nanowires, nanodots, and solid-state thermionic power generation devices.
Abstract: Recent advances in semiconductor thermoelectric physics and materials are reviewed. A key requirement to improve the energy conversion efficiency is to increase the Seebeck coefficient (S) and the electrical conductivity (σ) while reducing the electronic and lattice contributions to thermal conductivity (κe + κL). Some new physical concepts and nanostructures make it possible to modify the trade-offs between the bulk material properties through changes in the density of states, scattering rates, and interface effects on electron and phonon transport. We review recent experimental and theoretical results on nanostructured materials of various dimensions: superlattices, nanowires, nanodots, and solid-state thermionic power generation devices. Most of the recent success has been in the reduction of lattice thermal conductivity with the concurrent maintenance of good electrical conductivity. Several theoretical and experimental results to improve the thermoelectric power factor (S2σ) and to reduce the Lorenz ...
658 citations
TL;DR: In this article, the authors investigated the thermoelectric transport properties of p-type PbTe:Na, with high hole concentrations of approximately 1020 cm−3, from room temperature to 750 K. The greatly enhanced Seebeck coefficient at these doping levels can be understood by the presence of a sharp increase in the density of states around the Fermi level.
Abstract: Thermoelectric transport properties of p-type PbTe:Na, with high hole concentrations of approximately 1020 cm−3, are reinvestigated from room temperature to 750 K. The greatly enhanced Seebeck coefficient at these doping levels can be understood by the presence of a sharp increase in the density of states around the Fermi level. As a result, the thermoelectric figure of merit, zT, reaches ∼1.4 at 750 K. The influence of these heavy hole carriers may contribute to a similarly high zT observed in related p-type PbTe-based systems such as Tl-doped PbTe and nanostructured composite materials.
613 citations
TL;DR: Al-containing ZnO nanocomposites are reported with up to a factor of 20 lower κ(L) than non-nanostructured ZNO, while retaining bulklike α and σ, and holds promise for engineering advanced oxide-based high-ZT thermoelectrics for applications.
Abstract: ZnO is a promising high figure-of-merit (ZT) thermoelectric material for power harvesting from heat due to its high melting point, high electrical conductivity σ, and Seebeck coefficient α, but its practical use is limited by a high lattice thermal conductivity κL. Here, we report Al-containing ZnO nanocomposites with up to a factor of 20 lower κL than non-nanostructured ZnO, while retaining bulklike α and σ. We show that enhanced phonon scattering promoted by Al-induced grain refinement and ZnAl2O4 nanoprecipitates presages ultralow κ ∼ 2 Wm −1 K–1 at 1000 K. The high α∼ −300 μV K–1 and high σ ∼ 1–104 Ω–1 m–1 result from an offsetting of the nanostructuring-induced mobility decrease by high, and nondegenerate, carrier concentrations obtained via excitation from shallow Al donor states. The resultant ZT ∼ 0.44 at 1000 K is 50% higher than that for the best non-nanostructured counterpart material at the same temperature and holds promise for engineering advanced oxide-based high-ZT thermoelectrics for appl...
412 citations
TL;DR: The composites, containing single-wall carbon nanotubes, containing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and/or polyvinyl acetate, show thermopowers weakly correlated with electrical conductivities, resulting in large thermoelectric power factors in the in-plane direction of the composites which make them very promising for various electronic applications.
Abstract: Typical organic materials have low thermal conductivities that are best suited to thermoelectrics, but their poor electrical properties with strong adverse correlations have prevented them from being feasible candidates. Our composites, containing single-wall carbon nanotubes, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and/or polyvinyl acetate, show thermopowers weakly correlated with electrical conductivities, resulting in large thermoelectric power factors in the in-plane direction of the composites, ∼160 μW/m·K2 at room temperature, which are orders of magnitude larger than those of typical polymer composites. Furthermore, their high electrical conductivities, ∼105 S/m at room temperature, make our composites very promising for various electronic applications. The optimum nanotube concentrations for better power factors were identified to be 60 wt % with 40 wt % polymers. It was noticed that high nanotube concentrations above 60 wt % decreased the electrical conductivity of the composites ...
410 citations
TL;DR: Through a nanocomposite approach using ball milling and hot pressing, a peak ZT of 0.8 at 700 °C is achieved, which is about 60% higher than the best reported 0.5 and might be good enough for consideration for waste heat recovery in car exhaust systems.
Abstract: Half-Heuslers would be important thermoelectric materials due to their high temperature stability and abundance if their dimensionless thermoelectric figure of merit (ZT) could be made high enough. The highest peak ZT of a p-type half-Heusler has been so far reported about 0.5 due to the high thermal conductivity. Through a nanocomposite approach using ball milling and hot pressing, we have achieved a peak ZT of 0.8 at 700 °C, which is about 60% higher than the best reported 0.5 and might be good enough for consideration for waste heat recovery in car exhaust systems. The improvement comes from a simultaneous increase in Seebeck coefficient and a significant decrease in thermal conductivity due to nanostructures. The samples were made by first forming alloyed ingots using arc melting and then creating nanopowders by ball milling the ingots and finally obtaining dense bulk by hot pressing. Further improvement in ZT is expected when average grain sizes are made smaller than 100 nm.
372 citations
TL;DR: In this paper, thermal transport properties of n-type PbTe1−xIx with carrier concentrations ranging from 5.8 × 1018−1.4 × 1020 cm−3 are reinvestigated from room temperature to 800 K.
Abstract: Thermoelectric transport properties of n-type PbTe1−xIx with carrier concentrations ranging from 5.8 × 1018–1.4 × 1020 cm−3 are reinvestigated from room temperature to 800 K. The electronic transport properties, resistivity and Seebeck coefficient in this study are effectively consistent with prior reports, however the thermal conductivity has been found to be historically overestimated. The reassessment of the thermal transport properties, in combination with careful control of the carrier density by iodine doping, reveals a significantly larger figure of merit, zT ∼ 1.4, than often previously reported for n-type PbTe. The results and analysis of the data from this study lead to a redetermination of zT for this historical thermoelectric material and provide a renewed interest in n-type PbTe based materials.
366 citations
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TL;DR: In this article, the authors demonstrate the beneficial effect of light effective mass leading to high power factor 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 state (DOS) around the Fermi level 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 effective mass, which results in a simultaneous decrease of mobility. In fact, the net effect of high effective mass is a lower thermoelectric figure of merit when the carriers are predominantly scattered by acoustic phonons according to the deformation potential theory of Bardeen-Shockley. We demonstrate the beneficial effect of light effective mass leading to high power factor 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.
357 citations
TL;DR: The present study shows that artificial hole doping indeed enhances the conductivity of a metal-halide cubic perovskite, and is suggested to result from spontaneous hole-doping in the crystallization process, rather than the semi-metal electronic structure.
Abstract: The structural and electrical properties of a metal-halide cubic perovskite, CH3NH3SnI3, have been examined. The band structure, obtained using first-principles calculation, reveals a well-defined band gap at the Fermi level. However, the temperature dependence of the single-crystal electrical conductivity shows metallic behavior down to low temperatures. The temperature dependence of the thermoelectric power is also metallic over the whole temperature range, and the large positive value indicates that charge transport occurs with a low concentration of hole carriers. The metallic properties of this as-grown crystal are thus suggested to result from spontaneous hole-doping in the crystallization process, rather than the semi-metal electronic structure. The present study shows that artificial hole doping indeed enhances the conductivity.
333 citations
TL;DR: A high temperature Seebeck coefficient measurement apparatus with various features to minimize typical sources of error is designed and built, and suitable for bulk samples with a broad range of physical types and shapes.
Abstract: A high temperature Seebeck coefficient measurement apparatus with various features to minimize typical sources of error is designed and built. Common sources of temperature and voltage measurement error are described and principles to overcome these are proposed. With these guiding principles, a high temperature Seebeck measurement apparatus with a uniaxial 4-point contact geometry is designed to operate from room temperature to over 1200 K. This instrument design is simple to operate, and suitable for bulk samples with a broad range of physical types and shapes.
278 citations
TL;DR: The electrical conductivity and Seebeck coefficient of BiCu(1-x)SeO indicate that the carriers were introduced in the (Cu(2)Se(2))(2)- layer by Cu deficiencies, which makes it a promising candidate for medium temperature thermoelectric applications.
Abstract: A significant enhancement of thermoelectric performance in layered oxyselenides BiCuSeO was achieved. The electrical conductivity and Seebeck coefficient of BiCu(1-x)SeO (x = 0-0.1) indicate that the carriers were introduced in the (Cu(2)Se(2))(2-) layer by Cu deficiencies. The maximum of electrical conductivity is 3 × 10(3) S m(-1) for Bicu(0.975)Seo at 650 °C, much larger than 470 S m(-1) for pristine BiCuSeO. Featured with very low thermal conductivity (∼0.5 W m(-1) K(-1)) and a large Seebeck coefficient (+273 μV K(-1)), ZT at 650 °C is significantly increased from 0.50 for pristine BiCuSeO to 0.81 for BiCu(0.975)SeO by introducing Cu deficiencies, which makes it a promising candidate for medium temperature thermoelectric applications.
TL;DR: The magneto-Seebeck effect as mentioned in this paper is observed when a magnetic configuration changes the charge-based Seebeck coefficient, which can be measured as a voltage change directly without conversion of a spin current.
Abstract: Creating temperature gradients in magnetic nanostructures has resulted in a new research direction, that is, the combination of magneto- and thermoelectric effects. Here, we demonstrate the observation of one important effect of this class: the magneto-Seebeck effect. It is observed when a magnetic configuration changes the charge-based Seebeck coefficient. In particular, the Seebeck coefficient changes during the transition from a parallel to an antiparallel magnetic configuration in a tunnel junction. In this respect, it is the analogue to the tunnelling magnetoresistance. The Seebeck coefficients in parallel and antiparallel configurations are of the order of the voltages known from the charge-Seebeck effect. The size and sign of the effect can be controlled by the composition of the electrodes' atomic layers adjacent to the barrier and the temperature. The geometric centre of the electronic density of states relative to the Fermi level determines the size of the Seebeck effect. Experimentally, we realized 8.8% magneto-Seebeck effect, which results from a voltage change of about -8.7 μV K⁻¹ from the antiparallel to the parallel direction close to the predicted value of -12.1 μV K⁻¹. In contrast to the spin-Seebeck effect, it can be measured as a voltage change directly without conversion of a spin current.
TL;DR: In this article, a review of recent developments from thermoelectric model systems, e.g., nanowires, nanoscale meshes, up to nanograined bulk-materials, is discussed.
Abstract: Thermoelectric materials could play an increasing role for the efficient use of energy resources and waste heat recovery in the future. The thermoelectric efficiency of materials is described by the figure of merit ZT = (S2σT)/κ (S Seebeck coefficient, σ electrical conductivity, κ thermal conductivity, and T absolute temperature). In recent years, several groups worldwide have been able to experimentally prove the enhancement of the thermoelectric efficiency by reduction of the thermal conductivity due to phonon blocking at nanostructured interfaces. This review addresses recent developments from thermoelectric model systems, e.g. nanowires, nanoscale meshes, and thermionic superlattices, up to nanograined bulk-materials. In particular, the progress of nanostructured silicon and related alloys as an emerging material in thermoelectrics is emphasized. Scalable synthesis approaches of high-performance thermoelectrics for high-temperature applications is discussed at the end.
TL;DR: This work demonstrates the first solution-processable metal-semiconductor nanocomposites with enhanced thermoelectric properties via carrier energy filtering with the possibility of combining a diverse set of n- and p-type semiconductor matrices with nanocrystals to engineer and optimize energy-dependent carrier scattering with the ease of materials processing.
Abstract: This work demonstrates the first solution-processable metal–semiconductor nanocomposites with enhanced thermoelectric properties via carrier energy filtering. Platinum nanocrystals are embedded in a p-type antimony(III) telluride (Sb2Te3) semiconductor matrix, thus introducing band-bending potentials for holes. By scattering low energy holes, an increase in thermopower is observed. Introduction of Pt nanocrystals also increases carrier concentration thereby partially compensating for reduced electrical conductivity due to the decreased mobility. At room temperature, an improvement in thermoelectric power factor was achieved compared to that of the Sb2Te3 films. This work highlights the possibility of combining a diverse set of n- and p-type semiconductor matrices with nanocrystals to engineer and optimize energy-dependent carrier scattering with the ease of materials processing.
TL;DR: It is shown that the fractional area coverage of thermoelectric elements in a module could play a significant role in reducing the cost of power generation systems and power output per unit mass can be maximized.
Abstract: The energy conversion efficiency of today’s thermoelectric generators is significantly lower than that of conventional mechanical engines. Almost all of the existing research is focused on materials to improve the conversion efficiency. Here we propose a general framework to study the cost-efficiency trade-off for thermoelectric power generation. A key factor is the optimization of thermoelectric modules together with their heat source and heat sinks. Full electrical and thermal co-optimization yield a simple analytical expression for optimum design. Based on this model, power output per unit mass can be maximized. We show that the fractional area coverage of thermoelectric elements in a module could play a significant role in reducing the cost of power generation systems.
TL;DR: huge values of 7 mV/K at 0.1 M concentration for tetrabutylammonium nitrate in 1-dodecanol open the question of unexpectedly large kosmotrope or "structure making" effects of tetraalkylammonia ions on the structure of alcohols.
Abstract: The Seebeck coefficients of the nonaqueous electrolytes tetrabutylammonium nitrate, tetraoctylphosphonium bromide, and tetradodecylammonium nitrate in 1-octanol, 1-dodecanol, and ethylene-glycol are measured in a temperature range from T = 30 °C to T = 45 °C. The Seebeck coefficient is generally of the order of a few hundreds of microvolts per Kelvin for aqueous solution of inorganic ions. Here we report huge values of 7 mV/K at 0.1 M concentration for tetrabutylammonium nitrate in 1-dodecanol. These striking results open the question of unexpectedly large kosmotrope or “structure making” effects of tetraalkylammonium ions on the structure of alcohols.
TL;DR: In this article, a three-dimensional thermoelectric generator model is proposed and implemented in a computational fluid dynamics simulation environment (FLUENT), which accounts for all temperature dependent characteristics of the materials, and includes nonlinear fluid-thermal-electric multi-physics coupled effects.
TL;DR: In this paper, the authors investigated the effect of Bi (semimetal) nanoinclusions in nanostructured Bi 2 Te 3 matrices and showed that the incorporation of semimetal nanoparticles results in a reduction in the lattice thermal conductivity in all the samples.
Abstract: The effect of Bi (semimetal) nanoinclusions in nanostructured Bi 2 Te 3 matrices is investigated. Bismuth nanoparticles synthesized by a low temperature solvothermal method are incorporated into Bi 2 Te 3 matrix phases, synthesized by planetary ball milling. High density pellets of the Bi nanoparticle/Bi 2 Te 3 nanocomposites are created by hot pressing the powders at 200 ° C and 100 MPa. The effect of different volume fractions (0–7%) of Bi semimetal nanoparticles on the Seebeck coeffi cient, electrical conductivity, thermal conductivity and carrier concentration is reported. Our results show that the incorporation of semimetal nanoparticles results in a reduction in the lattice thermal conductivity in all the samples. A signifi cant enhancement in power factor is observed for Bi nanoparticle volume fraction of 5% and 7%. We show that it is possible to reduce the lattice thermal conductivity and increase the power factor resulting in an increase in fiof merit by a factor of 2 (from ZT = 0.2 to 0.4). Seebeck coeffi cient and electrical conductivity as a function of carrier concentration data are consistent with the electron fi ltering effect, where lowenergy electrons are preferentially scattered by the barrier potentials set up at the semimetal nanoparticle/semiconductor interfaces.
TL;DR: In this article, a new model of the magneto-thermoelasticity theory has been constructed in the context of a new consideration of heat conduction with fractional derivative.
Abstract: In this work, a new model of the magneto-thermoelasticity theory has been constructed in the context of a new consideration of heat conduction with fractional derivative. A one-dimensional application for a conducting half-space of thermoelectric elastic material, which is thermally shocked in the presence of a magnetic field, has been solved using Laplace transform and state-space techniques (Ezzat, 2008 [1]). According to the numerical results and its graphs, a conclusion about the new theory of magneto-thermoelasticity has been constructed. The theories of coupled magneto-thermoelasticity and of generalized magneto-thermoelasticity with one relaxation time follow as limited cases. The result provides a motivation to investigate conducting thermoelectric materials as a new class of applicable materials.
TL;DR: In this paper, coherent electron transport through zero-dimensional systems can be used to tailor the shape of the system's transmission function, which can enhance the performance of quantum dots or molecules in thermal-to-electric power conversion.
Abstract: We show that coherent electron transport through zero-dimensional systems can be used to tailor the shape of the system's transmission function. This quantum-engineering approach can be used to enhance the performance of quantum dots or molecules in thermal-to-electric power conversion. Specifically, we show that electron interference in a two-level system can substantially improve the maximum thermoelectric power and the efficiency at maximum power by suppressing parasitic charge flow near the Fermi energy and by reducing electronic heat conduction. We discuss possible realizations of this approach in molecular junctions or quantum dots.
TL;DR: The experiments and computational modeling indicate the prospect of tuning thermoelectric properties at the molecular scale, and the thiol-terminated aromatic molecular junctions revealed a positive thermopower that increased linearly with length.
Abstract: We present a combined experimental and computational study that probes the thermoelectric and electrical transport properties of molecular junctions. Experiments were performed on junctions created by trapping aromatic molecules between gold electrodes. The end groups (-SH, -NC) of the aromatic molecules were systematically varied to study the effect of contact coupling strength and contact chemistry. When the coupling of the molecule with one of the electrodes was reduced by switching the terminal chemistry from -SH to -H, the electrical conductance of molecular junctions decreased by an order of magnitude, whereas the thermopower varied by only a few percent. This has been predicted computationally in the past and is experimentally demonstrated for the first time. Further, our experiments and computational modeling indicate the prospect of tuning thermoelectric properties at the molecular scale. In particular, the thiol-terminated aromatic molecular junctions revealed a positive thermopower that increased linearly with length. This positive thermopower is associated with charge transport primarily through the highest occupied molecular orbital, as shown by our computational results. In contrast, a negative thermopower was observed for a corresponding molecular junction terminated by an isocyanide group due to charge transport primarily through the lowest unoccupied molecular orbital.
TL;DR: In this paper, the authors analyzed the thermal and electrical properties of perfect GNRs as a function of their width and their edge orientation to identify a strategy likely to degrade the thermal conductance while retaining high electronic conductance and thermopower.
Abstract: Strongly enhanced thermoelectric properties are predicted for graphene nanoribbons (GNRs) with optimized pattern By means of nonequilibrium Green's function atomistic simulation of electron and phonon transport, we analyze the thermal and electrical properties of perfect GNRs as a function of their width and their edge orientation to identify a strategy likely to degrade the thermal conductance while retaining high electronic conductance and thermopower An effect of resonant tunneling of electrons is detected in mixed GNRs consisting of alternate zigzag and armchair sections To fully benefit from this effect and from strongly reduced phonon thermal conductance, a structure with armchair and zigzag sections of different widths is proposed It is shown to provide a high thermoelectric factor of merit $\mathit{ZT}$ exceeding unity at room temperature
TL;DR: In this article, the lattice constants of RFe_(4)Sb_(12) increase almost linearly with increasing the ionic radii of the fillers, while the lattices expansion in filled structure is weakly influenced by the filler valence charge states.
Abstract: Fully filled skutterudites RFe_(4)Sb_(12) (R = Ca, Sr, Ba, La, Ce, Pr, Nd, Eu, and Yb) have been prepared and the high-temperature electrical and thermal transport properties are investigated systematically. Lattice constants of RFe_(4)Sb_(12) increase almost linearly with increasing the ionic radii of the fillers, while the lattice expansion in filled structure is weakly influenced by the filler valence charge states. Using simple charge counting, the hole concentration in RFe_(4)Sb_(12) with divalent fillers (R = Ca, Sr, Ba, Eu, and Yb) is much higher than that in RFe4Sb12 with trivalent fillers (R = La, Ce, Pr, and Nd), resulting in relatively high electrical conductivity and low Seebeck coefficient. It is also found that RFe_(4)Sb_(12) filled skutterudites having similar filler valence charge states exhibit comparable electrical conductivity and Seebeck coefficient, and the behavior of the temperature dependence, thereby leading to comparable power factor values in the temperature range from 300 to 800 K. All RFe_(4)Sb_(12) samples possess low lattice thermal conductivity. The correlation between the lattice thermal resistivity WL and ionic radii of the fillers is discussed and a good relationship of W_L ~ (r_(cage)−r_(ion))^3 is observed in lanthanide metal filled skutterudites. CeFe_(4)Sb_(12), PrFe_(4)Sb_(12), and NdFe_(4)Sb_(12) show the highest thermoelectric figure of merit around 0.87 at 750 K among all the filled skutterudites studied in this work.
TL;DR: Measurement of Seebeck coefficients in a range of ionic liquids (ILs) suggests that these electrolytes could enable the development of thermoelectric devices to generate electrical energy from low-grade heat in the 100-150 °C range.
TL;DR: The amplitude of the spin-Seebeck effect in GaMnAs scales with the thermal conductivity of theGaAs substrate and the phonon-drag contribution to the thermoelectric power of the GaMmAs, demonstrating that phonons drive the spin redistribution.
Abstract: Here we report on measurements of the spin-Seebeck effect in GaMnAs over an extended temperature range alongside the thermal conductivity, specific heat, magnetization, and thermoelectric power. The amplitude of the spin-Seebeck effect in GaMnAs scales with the thermal conductivity of the GaAs substrate and the phonon-drag contribution to the thermoelectric power of the GaMnAs, demonstrating that phonons drive the spin redistribution. A phenomenological model involving phonon-magnon drag explains the spatial and temperature dependence of the measured spin distribution.
TL;DR: In this paper, the current aspects of oxide thermoelectric materials, and some strategies of nanostructure control for selective reduction of the lattice thermal conductivity (selective phonon scattering) in bulk oxide ceramics are also discussed.
Abstract: Rapid progress in thermoelectric performance of oxide materials has been conducted virtually exclusively in Japan, resulting in more than 10 times increase in the ZT values of oxides within the last two decades. This has caused a revolutionary change in the guiding principles of thermoelectric materials research, in which oxide materials had been disregarded as a potential candidate until early 1990s. Promising oxide thermoelectric materials having been discovered include CaMnO3-based perovskites, Al-doped ZnO, layered cobalt oxides represented by NaCo2O4 and Ca3Co4O9, and SrTiO3-related phases. This paper reviews the current aspects of oxide thermoelectric materials, and some strategies of nanostructure control for selective reduction of the lattice thermal conductivity (selective phonon scattering) in bulk oxide ceramics will also be discussed.
TL;DR: In this article, the authors investigated the thermal and electronic transport properties of half-Heusler (HH) phases for enhancing the dimensionless figure of merit (ZT) at 800-1000 K.
Abstract: Half-Heusler (HH) phases, a versatile class of alloys with promising functional properties, have recently gained attention as emerging thermoelectric materials. These materials are investigated from the perspective of thermal and electronic transport properties for enhancing the dimensionless figure of merit (ZT) at 800–1000 K. The electronic origin of thermopower enhancement is reviewed. Grain refinement and embedment of nanoparticles in HH alloy hosts were used to produce fine-grained as well as nanocomposites and monolithic nanostructured materials. Present experiments indicated that n-type Hf0.6Zr0.4NiSn0.995Sb0.005 HH alloys and p-type Hf0.3Zr0.7CoSn0.3Sb0.7/nano-ZrO2 composites can attain ZT = 1.05 and 0.8 near 900–1000 K, respectively. The observed ZT enhancements could be attributed to multiple origins; in particular, the electronic origin was identified. The prospect for higher ZT was investigated in light of a recently developed nanostructure model of lattice thermal conductivity. Tests performed on p–n couple devices from the newly developed HH materials showed good power generation efficiencies—achieving 8.7% efficiency for hot-side temperatures of about 700 °C.
TL;DR: In this paper, the Seeebeck coefficient of tetraalkylammonium ion in 1-dodecanol was found to be 7 mV/K at 0.1M concentration.
Abstract: The Seeebeck coefficients of the non-aqueous electrolytes tetrabutylammonium nitrate, tetraoctylphosphonium bromide and tetradodecylammonium nitrate in 1-octanol, 1-dodecanol and ethylene-glycol are measured in a temperature range from T=30 to T=45 C. The Seebeck coefficient is generally of the order of a few hundreds of microvolts per Kelvin for aqueous solution of inorganic ions. Here we report huge values of 7 mV/K at 0.1M concentration for tetrabutylammonium nitrate in 1-dodecanol. These striking results open the question of unexpectedly large kosmotrope or "structure making" effects of tetraalkylammonium ions on the structure of alcohols.
TL;DR: In this article, the authors investigated the electronic and thermal transport properties of graphene antidot lattices with a finite length along the transport direction, and they showed that both the thermal and electronic transport properties converge fast toward the bulk limit with increasing length of the lattice.
Abstract: We present calculations of the electronic and thermal transport properties of graphene antidot lattices with a finite length along the transport direction. The calculations are based on the $\ensuremath{\pi}$-tight-binding model and the Brenner potential. We show that both electronic and thermal transport properties converge fast toward the bulk limit with increasing length of the lattice: only a few repetitions ($\ensuremath{\simeq}$6) of the fundamental unit cell are required to recover the electronic band gap of the infinite lattice as a transport gap for the finite lattice. We investigate how different antidot shapes and sizes affect the thermoelectric properties. The resulting thermoelectric figure of merit, $ZT$, can exceed $0.25$, and it is highly sensitive to the atomic arrangement of the antidot edges. Specifically, hexagonal holes with pure armchair edges lead to an order-of-magnitude larger $ZT$ as compared to pure zigzag edges. We explain this behavior as a consequence of the localization of states, which predominantly occurs for zigzag edges, and of an increased splitting of the electronic minibands, which reduces the power factor ${S}^{2}{G}_{e}$ ($S$ is the Seebeck coefficient and ${G}_{e}$ is the electric conductance).
TL;DR: In this article, a review of recent efforts on improving thermoelectric efficiency is presented, and several novel proof-of-principle approaches such as phonon disorder in phonon-glasselectron crystals, low dimensionality in nanostructured materials and charge-spin-orbital degeneracy in strongly correlated systems are discussed.
Abstract: By converting waste heat into electricity through the thermoelectric power of solids without producing greenhouse gas emissions, thermoelectric generators could be an important part of the solution to today's energy challenge. There has been a resurgence in the search for new materials for advanced thermoelectric energy conversion applications. In this paper, we will review recent efforts on improving thermoelectric efficiency. Particularly, several novel proof-of-principle approaches such as phonon disorder in phonon-glasselectron crystals, low dimensionality in nanostructured materials and charge-spin-orbital degeneracy in strongly correlated systems on thermoelectric performance will be discussed.