Showing papers on "Seebeck coefficient published in 2013"
TL;DR: Reducing dopant volume is found to be as important as optimizing carrier concentration when maximizing ZT in OSCs, and this stands in sharp contrast to ISCs, for which these parameters have trade-offs.
Abstract: The conversion efficiency of heat to electricity in thermoelectric materials depends on both their thermopower and electrical conductivity. It is now reported that, unlike their inorganic counterparts, organic thermoelectric materials show an improvement in both these parameters when the volume of dopant elements is minimized; furthermore, a high conversion efficiency is achieved in PEDOT:PSS blends.
1,366 citations
TL;DR: A large and tunable Seebeck coefficient of the single-layer MoS(2) paves the way to new applications of this material such as on-chip thermopower generation and waste thermal energy harvesting.
Abstract: We study the photoresponse of single-layer MoS(2) field-effect transistors by scanning photocurrent microscopy. We find that, unlike in many other semiconductors, the photocurrent generation in single-layer MoS(2) is dominated by the photothermoelectric effect and not by the separation of photoexcited electron-hole pairs across the Schottky barriers at the MoS(2)/electrode interfaces. We observe a large value for the Seebeck coefficient for single-layer MoS(2) that by an external electric field can be tuned between -4 × 10(2) and -1 × 10(5) μV K(-1). This large and tunable Seebeck coefficient of the single-layer MoS(2) paves the way to new applications of this material such as on-chip thermopower generation and waste thermal energy harvesting.
541 citations
TL;DR: In this paper, the synthesis methods for optimizing individual parameters to enhance the thermoelectric performance in both MNiSn and MCoSb based half-Heuslers are summarized.
488 citations
01 Jan 2013
TL;DR: In this article, the photoresponse of single-layer MoS2 field effect transistors was studied by scanning photocurrent microscopy and it was shown that the photothermoelectric effect is dominant over the separation of photoexcited electron−hole pairs across the Schottky barriers at the MoS 2/electrode interfaces.
Abstract: We study the photoresponse of single-layer MoS2 field- effect transistors by scanning photocurrent microscopy. We find that, unlike in many other semiconductors, the photocurrent generation in single-layer MoS2 is dominated by the photothermoelectric effect and not by the separation of photoexcited electron−hole pairs across the Schottky barriers at the MoS2/electrode interfaces. We observe a large value for the Seebeck coefficient for single-layer MoS2 that by an external electric field can be tuned between −4 × 10 2 and −1 × 10 5 μ VK −1 . This large and tunable Seebeck coefficient of the single-layer MoS2 paves the way to new applications of this material such as on- chip thermopower generation and waste thermal energy harvesting.
486 citations
TL;DR: In this article, the photoresponse of single-layer MoS2 field effect transistors was studied by scanning photocurrent microscopy and it was shown that the photocurrent generation in single layer MOS2 is dominated by the photo-thermoelectric effect and not by the separation of photoexcited electron-hole pairs across the Schottky barriers at the MoS 2/electrode interfaces.
Abstract: We study the photoresponse of single-layer MoS2 field-effect transistors by scanning photocurrent microscopy. We find that, unlike in many other semiconductors, the photocurrent generation in single-layer MoS2 is dominated by the photo-thermoelectric effect and not by the separation of photoexcited electron-hole pairs across the Schottky barriers at the MoS2/electrode interfaces. We observe a large value for the Seebeck coefficient for single-layer MoS2 that, by an external electric field, can be tuned between -4x10^2 uV/K and -1x10^5 uV/K. This large and tunable Seebeck coefficient of the single-layer MoS2 paves the way to new applications of this material such as on-chip thermopower generation and waste thermal energy harvesting.
447 citations
TL;DR: The first experimental verification of the spin gapless magnetic semiconductor Mn(2)CoAl, an inverse Heusler compound with a Curie temperature of 720 K and a magnetic moment of 2 μ(B) is reported.
Abstract: Recent studies have reported an interesting class of semiconductor materials that bridge the gap between semiconductors and half-metallic ferromagnets. These materials, called spin gapless semiconductors, exhibit a band gap in one of the spin channels and a zero band gap in the other and thus allow for tunable spin transport. Here, we report the first experimental verification of the spin gapless magnetic semiconductor Mn(2)CoAl, an inverse Heusler compound with a Curie temperature of 720 K and a magnetic moment of 2 μ(B). Below 300 K, the compound exhibits nearly temperature-independent conductivity, very low, temperature-independent carrier concentration, and a vanishing Seebeck coefficient. The anomalous Hall effect is comparatively low, which is explained by the symmetry properties of the Berry curvature. Mn(2) CoAl is not only suitable material for room temperature semiconductor spintronics, the robust spin polarization of the spin gapless semiconductors makes it very promising material for spintronics in general.
399 citations
TL;DR: In this article, it is demonstrated that mixing SiC nanoparticles into the BiSbTe matrix effectively enhances its thermoelectric properties; a high dimensionless figure of merit (ZT) value of up to 1.33 at 373 K is obtained in Bi0.3Sb1.7Te3 incorporated with only 0.4 vol% SiC nanoinclusions possessing coherent interfaces with the Bi 0.
Abstract: Thermoelectric materials have potential applications in energy harvesting and electronic cooling devices, and bismuth antimony telluride (BiSbTe) alloys are the state-of-the-art thermoelectric materials that have been widely used for several decades. It is demonstrated that mixing SiC nanoparticles into the BiSbTe matrix effectively enhances its thermoelectric properties; a high dimensionless figure of merit (ZT) value of up to 1.33 at 373 K is obtained in Bi0.3Sb1.7Te3 incorporated with only 0.4 vol% SiC nanoparticles. SiC nanoinclusions possessing coherent interfaces with the Bi0.3Sb1.7Te3 matrix can increase the Seebeck coefficient while increasing the electrical conductivity, in addition to its effect of reducing lattice thermal conductivity by enhancing phonon scattering. Nano-SiC dispersion further endows the BiSbTe alloys with better mechanical properties, which are favorable for practical applications and device fabrication.
390 citations
TL;DR: Zhao et al. as discussed by the authors reported on the high thermoelectric performance of p-type polycrystalline BiCuSeO, a layered oxyselenide composed of alternating conductive and insulating (Bi2O2)2+ layers.
Abstract: We report on the high thermoelectric performance of p-type polycrystalline BiCuSeO, a layered oxyselenide composed of alternating conductive (Cu2Se2)2− and insulating (Bi2O2)2+ layers. The electrical transport properties of BiCuSeO materials can be significantly improved by substituting Bi3+ with Ca2+. The resulting materials exhibit a large positive Seebeck coefficient of ∼+330 μV K−1 at 300 K, which may be due to the ‘natural superlattice’ layered structure and the moderate effective mass suggested by both electronic density of states and carrier concentration calculations. After doping with Ca, enhanced electrical conductivity coupled with a moderate Seebeck coefficient leads to a power factor of ∼4.74 μW cm−1 K−2 at 923 K. Moreover, BiCuSeO shows very low thermal conductivity in the temperature range of 300 (∼0.9 W m−1 K−1) to 923 K (∼0.45 W m−1 K−1). Such low thermal conductivity values are most likely a result of the weak chemical bonds (Young’s modulus, E∼76.5 GPa) and the strong anharmonicity of the bonding arrangement (Gruneisen parameter, γ∼1.5). In addition to increasing the power factor, Ca doping reduces the thermal conductivity of the lattice, as confirmed by both experimental results and Callaway model calculations. The combination of optimized power factor and intrinsically low thermal conductivity results in a high ZT of ∼0.9 at 923 K for Bi0.925Ca0.075CuSeO. Li-Dong Zhao, Jiaqing He and co-workers have gained insight into the highly thermoelectric properties of a bismuth–copper oxyselenide (BiCuSeO), a polycrystalline, layered compound. BiCuSeO's ability to produce a significant electric potential from a temperature difference, and vice versa, arises from its intrinsically low thermal conductivity, and can be further improved by boosting the material's electrical conductivity through doping with strontium or barium, or introducing copper deficiencies. The researchers have now carried out an extensive characterization of the oxyselenide and propose that its conveniently low thermal conductivity results from the weak chemical bonds that exist between two different kinds of layers, and a particular bonding arrangement, in the material's lattice. Moreover, by substituting bismuth ions (Bi3+) with calcium ions (Ca3+) the thermal conductivity of the lattice could be lowered further, leading to an improvement in the oxyselenide's thermoelectric properties. We report on the promising thermoelectric performance of p-type polycrystalline BiCuSeO, which is a layered oxyselenide composed of conductive (Cu2Se2)2− layers that alternate with insulating (Bi2O2)2+ layers. Electrical transport properties can be optimized by substituting Bi3+ with Ca2+. Moreover, BiCuSeO shows very low thermal conductivity in the temperature ranges of 300 (∼0.9 W m−1K−1) to 923 K (∼0.45 W m−1 K−1). These intrinsically low thermal conductivity values may result from the weak chemical bonds of the material as well as the strong anharmonicity of the bonding arrangement. The combination of the optimized power factor and the intrinsically low thermal conductivity results in a high ZT of ∼0.9 at 923 K for Bi0.925Ca0.075CuSeO.
327 citations
TL;DR: Noncovalently functionalized graphene with fullerene by π-π stacking in a liquid-liquid interface was integrated into poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) to achieve synergistic effect on enhancing thermoelectric properties.
Abstract: Organic thermoelectric (TE) materials are very attractive due to easy processing, material abundance and environmentally-benign characteristics, but their potential is significantly restricted by the inferior thermoelectric properties. In this work, noncovalently functionalized graphene with fullerene by π-π stacking in a liquid-liquid interface was integrated into poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate). Graphene helps to improve electrical conductivity while fullerene enhances the Seebeck coefficient and hinders thermal conductivity, resulting in the synergistic effect on enhancing thermoelectric properties. With the integration of nanohybrids, the electrical conductivity increased from ~10000 to ~70000 S/m, the thermal conductivity changed from 0.2 to 2 W·K−1m−1 while the Seebeck coefficient was enhanced by around 4-fold. As a result, nanohybrids-based polymer composites demonstrated the figure of merit (ZT) as high as 6.7 × 10−2, indicating an enhancement of more than one order of magnitude in comparison to single-phase filler-based polymer composites with ZT at the level of 10−3.
308 citations
TL;DR: In this paper, the thermoelectric properties of poly(3,4-ethylenedioxylthiophene):poly(styrene sulfonate) (PEDOT:PSS) thin films at room temperature are studied.
Abstract: In this work, the thermoelectric (TE) properties of poly(3,4-ethylenedioxylthiophene):poly(styrene sulfonate) (PEDOT:PSS) thin films at room temperature are studied. Different methods have been applied for tuning the TE properties: 1st addition of polar solvent, dimethyl sulfoxide (DMSO), into the PEDOT:PSS solution; 2nd post-treatment of thin films with a mixture of DMSO and ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4). It is verified that DMSO post-treatment is more efficient than DMSO addition in improving the electrical conductivity with a trivial change in the Seebeck coefficient. The power factor is increased up to 30.1 μW mK−2 for the film with DMSO post-treatment, while the optimized power factor by DMSO addition is 18.2 μW mK−2. It is shown that both DMSO addition and post-treatment induce morphological changes: an interconnected network of elongated PEDOT grains is generated, leading to higher electrical conductivity. In contrast, for those films post-treated in the presence of EMIMBF4, an interconnected network of short and circular PEDOT grains with increased polaron density is created, resulting in the improvement in the Seebeck coefficient and a concomitant compromise in the electrical conductivity. An optimized power factor of 38.46 μW mK−2 is achieved at 50 vol% of EMIMBF4, which is the highest reported so far for PEDOT:PSS thin films to our knowledge. Assuming a thermal conductivity of 0.17 W mK−1, the corresponding ZT is 0.068 at 300 K. These results demonstrate that post-treatment is a promising approach to enhance the TE properties of PEDOT:PSS thin films. Furthermore, ionic liquid, EMIMBF4, shows the potential for tuning the TE properties of PEDOT:PSS thin films via a more environmentally benign process.
295 citations
TL;DR: In this paper, the authors investigated low and high temperature thermoelectric properties by measuring the electrical conductivity, Seebeck coefficient, thermal conductivity and Hall coefficient between 2 K and 900 K.
Abstract: Cu2Se, Cu2Te and Ag-overstoichiometric compounds Cu1.98Ag0.2Se and Cu1.98Ag0.2Te were prepared by melting, annealing, followed by spark plasma sintering compaction. Low and high temperature thermoelectric properties were investigated by measuring the electrical conductivity, Seebeck coefficient, thermal conductivity and Hall coefficient between 2 K and 900 K. Structural analyses were performed by PXRD and SEM-EDX analyses. The Hall and Seebeck coefficients show that holes are the dominant carrier in all compounds. High temperature α–β phase transition in Cu2Se and Cu1.98Ag0.2Se between 350 and 400 K and multiple phase transitions (α–β, β–γ, γ–δ, δ–∈) in Cu2Te and Cu1.98Ag0.2Te between 350 K and 900 K were observed in measurements of heat capacity, temperature dependent PXRD data, and transport coefficients. Low temperature transport measurements (Hall coefficient, electrical conductivity, carrier mobility) strongly suggest the presence of yet another phase transition in Cu2Se, Cu1.98Ag0.2Se, and Cu1.98Ag0.2Te compounds at temperatures between 85 K and 115 K, reported here for the first time. Based on the transport data and structural analysis we conclude that doping Cu2Se and Cu2Te by Ag reduces the density of holes and strongly suppresses the thermal conductivity not only due to a smaller electronic contribution but also due to enhanced point defect scattering of phonons that reduces the lattice portion of the thermal conductivity. Moreover, the phase transition temperature is shifted to lower temperatures upon doping with Ag. The presence of Ag enhances thermoelectric performance of Cu2Te at all temperatures and Cu2Se benefits from Ag doping over a broad range of temperatures up to 700 K. The maximum ZT value of 1.2 at 900 K; 0.52 at 650 K; 0.29 at 900 K; and 1.0 at 900 K were achieved for Cu2Se, Cu1.98Ag0.2Se, Cu2Te and Cu1.98Ag0.2Te, respectively, between 2 K and 900 K.
TL;DR: In this article, the power generation characteristics of thermoelectrochemical cells using a series of ionic liquids and MPN with the CoII/III(bpy)3(NTf2)2/3 couple are described.
Abstract: Manipulation of the cobalt(II/III) tris(bipyridyl) redox couple through anion exchange has improved its solubility in ionic liquids and 3-methoxypropionitrile (MPN). This has allowed the preparation of electrolytes with high Seebeck coefficients, Se = 1.5–2.2 mV K−1, and thereby excellent prospects for thermal harvesting. The unique physical properties of ionic liquids offer ideal characteristics for their use as electrolytes in thermoelectrochemical cells, particularly for applications involving thermal energy available at temperatures in the 100–200 °C range. The power generation characteristics of thermoelectrochemical cells using a series of ionic liquids and MPN with the CoII/III(bpy)3(NTf2)2/3 couple are described. Power densities reached >0.5 W m−2 in unoptimized devices, operating with a 130 °C hot side. The high Seebeck coefficient appears to have its origins in the high-to-low spin transition upon electron transfer in this cobalt complex.
TL;DR: Based on Fourier's law and the Seebeck effect, the authors in this article presented a mathematical model of a TEG device using the exhaust gas of vehicles as heat source, and the results showed that the output power and efficiency increase significantly by changing the convection heat transfer coefficient of the high temperature side than that of low temperature side.
TL;DR: In this paper, the thermal conduction of monolayer MoS2 sheet and nanoribbons using molecular dynamics simulations was investigated, and the thermal conductivity of MoS 2 was found to be 1.35 W/mK, which is three orders of magnitude lower than that of graphene.
Abstract: We investigated the thermal conduction of monolayer MoS2 sheet and nanoribbons using molecular dynamics simulations. Room temperature thermal conductivity of monolayer MoS2 is found to be 1.35 W/mK, which is three orders of magnitude lower than that of graphene. In contrast to the remarkable size effect observed in graphene nanoribbons, the thermal conductivity of MoS2 nanoribbons is insensitive to width (3–16 nm), length (4–111 nm), and the type of edge, which are explained by the local heat flux analysis and phonon scattering mechanisms. The low thermal conductivity together with reported high Seebeck coefficient opens up the possibility to realize MoS2-based two-dimensional thermoelectric devices.
TL;DR: The thermoelectric properties of a unique hybrid polymer-inorganic nanoparticle system consisting of tellurium nanowires and a conducting polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), can be optimized by both controlling the shape of the nanoparticles and the loading and doping of the polymeric matrix with polar solvents.
Abstract: The thermoelectric properties of a unique hybrid polymer–inorganic nanoparticle system consisting of tellurium nanowires and a conducting polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), can be optimized by both controlling the shape of the nanoparticles and the loading and doping of the polymeric matrix with polar solvents. The mechanism for an observed improvement in power factor is attributed to the unique conducting nature of PEDOT:PSS, which exhibits a transition from a hopping transport-dominated regime to a carrier scattering-dominated regime upon doping with polar solvents. Near this transition, the electrical conductivity can be improved without significantly reducing the thermopower. Relying on this principle, the power factor optimization for this new thermoelectric material is experimentally carried out and found to exceed 100 μW m−1 K−2, which is nearly five orders of magnitude greater than pure PEDOT:PSS.
TL;DR: In this paper, the authors compared the accuracy of simplified models with more accurate models, such as models based on an electrical analogy and on the finite element method (FEM), and showed that the key point is to use a null Thomson coefficient when a constant Seebeck coefficient is defined.
TL;DR: In this article, a theoretical analysis of a thermoelectric power generator is carried out and influence of the shape parameter on the device efficiency and power generation is formulated, and the geometric configuration of the legs in the device is associated with the shape parameters and incorporated in the analysis.
TL;DR: In this paper, a detailed theory on electron energy filtering by the nonplanar potential introduced by dispersed nanoparticles or impurities in bulk materials for enhancement of the thermoelectric power factor is presented.
Abstract: We present a detailed theory on electron energy filtering by the nonplanar potential introduced by dispersed nanoparticles or impurities in bulk materials for enhancement of the thermoelectric power factor. When electrons with energies below a certain cut-off energy are prevented from participating in conduction through the material, the Seebeck coefficient and thus the thermoelectric power factor can be drastically enhanced. Instead of using planar heterostructures which require elaborate epitaxial techniques, we study embedded nanoparticles or impurities so that the conservation of lateral momentum limiting electron transport at heterointerfaces is no longer a limiting factor. Based on the Boltzmann transport equations under the relaxation time approximation, the optimal cut-off energy level that maximizes the power factor is calculated to be a few ${k}_{B}T$ above the Fermi level, and is a function of the scattering parameter, Fermi level, and temperature. The maximized power factor enhancement is quantified as a function of those parameters. The electronic thermal conductivity and Lorenz number are also shown to be suppressed by the electron filtering to further enhance the thermoelectric figure of merit. We find that the power factor of PbTe at 300 K could be enhanced by more than 120$%$ when the cut-off energy level is 0.2 eV or higher and the carrier density higher than $5\ifmmode\times\else\texttimes\fi{}{10}^{19}$ cm${}^{\ensuremath{-}3}$. Finally we propose the use of distributed resonant scatterings to partially realize the nonplanar electron filtering in bulk materials.
TL;DR: In this article, the thermoelectric properties of the carrier-doped chalcopyrite alloys, Cu1-xFe1+xS2 with x = 0.03 and 0.05, and Zn0.03Cu0.97FeS2, were investigated.
Abstract: The chalcopyrite CuFeS2 is a natural magnetic semiconductor, where Fe spins order antiferromagnetically at TN = 853 K. We investigate the thermoelectric properties of the carrier-doped chalcopyrite alloys, Cu1-xFe1+xS2 with x = 0.03 and 0.05, and Zn0.03Cu0.97FeS2. All systems showed characteristic behavior of n-type degenerate semiconductors. The large Seebeck coefficient with a high carrier-density indicates enhanced carrier mass of m* = 3–6m0, where m0 is the electron mass. Consequently, the thermoelectric power factor exceeds 1×10-3 W K-2 m-1 at 400 K. We propose that utilizing magnetic semiconductor can be a new effective strategy to obtain enhanced values of the power factor.
TL;DR: It is shown that the thermoelectric response of the bulk states displays features specific to the Dirac spectrum, and that the first (N=0) Landau level is non-degenerate.
Abstract: Topological surface states in lead-doped tin selenide are assumed to arise from massive Dirac states in the bulk, but this has not been demonstrated to date. Using thermoelectric transport measurements, Liang et al. now close this gap, and further show a sign anomaly in the Nernst signal due to band inversion.
TL;DR: A microdevice was used to measure the in-plane thermoelectric properties of suspended bismuth telluride nanoplates, revealing a suppressed Seebeck coefficient together with a general trend of decreasing electrical conductivity and thermal conductivity with decreasing thickness.
Abstract: A microdevice was used to measure the in-plane thermoelectric properties of suspended bismuth telluride nanoplates from 9 to 25 nm thick. The results reveal a suppressed Seebeck coefficient together with a general trend of decreasing electrical conductivity and thermal conductivity with decreasing thickness. While the electrical conductivity of the nanoplates is still within the range reported for bulk Bi2Te3, the total thermal conductivity for nanoplates less than 20 nm thick is well below the reported bulk range. These results are explained by the presence of surface band bending and diffuse surface scattering of electrons and phonons in the nanoplates, where pronounced n-type surface band bending can yield suppressed and even negative Seebeck coefficient in unintentionally p-type doped nanoplates.
TL;DR: In this paper, the effect of Mg doping on the thermoelectric properties of p-type BiCuSeO oxyselenide, with layer structure composed of conductive (Cu 2 Se 2 2− layers alternately stacked with insulating (Bi 2 O 2 ) 2+ layers.
TL;DR: It is shown that transport takes place through two phases so that high conductivity is achieved in the grains, and high Seebeck coefficient by the grain boundaries, which together with the drastic reduction in the thermal conductivity due to boundary scattering could lead to a significant increase of the figure of merit ZT.
Abstract: A large thermoelectric power factor in heavily boron-doped p-type nanograined Si with grain sizes ~30 nm and grain boundary regions of ~2 nm is reported. The reported power factor is ~5 times higher than in bulk Si. It originates from the surprising observation that for a specific range of carrier concentrations, the electrical conductivity and Seebeck coefficient increase simultaneously. The two essential ingredients for this observation are nanocrystallinity and extremely high boron doping levels. This experimental finding is interpreted within a theoretical model that considers both electron and phonon transport within the semiclassical Boltzmann approach. It is shown that transport takes place through two phases so that high conductivity is achieved in the grains, and high Seebeck coefficient by the grain boundaries. This together with the drastic reduction in the thermal conductivity due to boundary scattering could lead to a significant increase of the figure of merit ZT. This is one of the rare observations of a simultaneous increase in the electrical conductivity and Seebeck coefficient, resulting in enhanced thermoelectric power factor.
TL;DR: The shown analysis can be used to find and minimize errors in the Seebeck coefficient measurement and therefore increase the reliability of the measured material properties.
Abstract: The Seebeck coefficient is one of the key quantities of thermoelectric materials and routinely measured in various laboratories There are, however, several ways to calculate the Seebeck coefficient from the raw measurement data We compare these different ways to extract the Seebeck coefficient, evaluate the accuracy of the results, and show methods to increase this accuracy We furthermore point out experimental and data analysis parameters that can be used to evaluate the trustworthiness of the obtained result The shown analysis can be used to find and minimize errors in the Seebeck coefficient measurement and therefore increase the reliability of the measured material properties
TL;DR: In this article, a two-step solid state reaction followed by spark plasma sintering consolidation was used to obtain the thermoelectric performance of Bi-doped Mg2Si0.4Sn0.6 solid solutions.
TL;DR: In this article, the effect of Ca substitution on microstructure and thermoelectric transport properties of BiCuSeO oxyselenide has been studied, where the substitution of Ca2+ for Bi3+ reduces both electrical resistivity and Seebeck coefficient due to an increased carrier concentration.
Abstract: The effect of Ca substitution on microstructure and thermoelectric transport properties of BiCuSeO oxyselenide has been studied. The substitution of Ca2+ for Bi3+ reduces both electrical resistivity and Seebeck coefficient due to an increased carrier concentration. However, the enhanced electrical conductivity compensates for the decrease of Seebeck coefficient, and consequently the power factor is greatly improved in the whole temperature range from 300 to 773 K, exceeding 600 μW m−1 K−2 in the Bi1−xCaxCuSeO samples with 0.075 ≤ x ≤ 0.125. Additionally, the lattice thermal conductivity is significantly reduced due to the refined grains and the introduced point defects that limit the phonon mean free path, resulting in a total thermal conductivity lower than 1.0 W m−1 K−1 in all the doped samples. Benefiting from the enhanced electrical conductivity and the reduced thermal conductivity, high ZT values, both at low and medium temperatures, 0.3 at 300 K and 0.8 at 773 K, are achieved for the Bi0.925Ca0.075CuSeO composition.
TL;DR: The thermoelectric performance of intrinsic n-type AgBiSe2, a Pb-free material with more earth-abundant and cheaper elements than intrinsic p-type homologous AgSbTe2, is reported on, which makes it a promising n- type candidate for medium-temperature TE applications.
Abstract: We report on the thermoelectric (TE) performance of intrinsic n-type AgBiSe2, a Pb-free material with more earth-abundant and cheaper elements than intrinsic p-type homologous AgSbTe2. Pb doping changes n-type AgBiSe2 to p-type but leads to poor electrical transport properties. Nb doping enhances the TE properties of n-type AgBiSe2 by increasing the carrier concentration. As a result of the intrinsically low thermal conductivity (0.7 W m(-1) K(-1)), low electrical resistivity (5.2 mΩ cm), and high absolute Seebeck coefficient (-218 μV/K), the TE figure of merit (ZT) at 773 K is significantly increased from 0.5 for solid-state-synthesized pristine AgBiSe2 to 1 for Ag0.96Nb0.04BiSe2, which makes it a promising n-type candidate for medium-temperature TE applications.
TL;DR: In this paper, the thermoelectric properties of high energy ball-milled powders were investigated as a function of the ball milling time and the fine grain sizes were confirmed with the X-ray analysis and the microscopy images in the samples fabricated with powders from long-running time.
TL;DR: The kilogram-grade production technique coupled with the high ZT makes metal nanoparticle decorated n-type materials very promising for commercial applications, and the concept of 'nanoparticle-in-alloy' to separately tune the electrical and thermal transport properties.
Abstract: In this study, n-type Cu and Zn metal nanoparticle decorated Bi2(Te0.9Se0.1)3 ingots were prepared by a large-scale zone melting technique, with the concept of ‘nanoparticle-in-alloy’ to separately tune the electrical and thermal transport properties. Cu and Zn additions play multiple but different roles in the materials, whereas both of them form metal nanoinclusions embedded in van der Waals gaps or grain boundaries, exerting influences on thermoelectric properties. Cu addition, accommodated in the tetrahedral vacancies formed by four Te(1) atoms, effectively adjusts the electron concentration by donating its valence electron, and appreciably optimizes the power factor. Coupled with the significant frustration of heat-carrying phonons by Cu nanoinclusions, a highest ZT of 1.15 can be achieved for the 1 at.% Cu sample, which is an ∼20% improvement compared with that of commercial halogen-doped ingots. Zn addition, however, acting as weak donor, noticeably increases the density of state effective mass and Seebeck coefficient, and gives rise to a high ZT of 1.1. In particular, the kilogram-grade production technique coupled with the high ZT makes metal nanoparticle decorated n-type materials very promising for commercial applications.
TL;DR: In this article, a thermoelectric module is subjected to thermal cycling and the authors evaluate the evolution of its performance through measurements of the temperature coefficient, electrical conductivity, and its individual components.
Abstract: Thermoelectric modules experience performance reduction and mechanical failure due to thermomechanical stresses induced by thermal cycling. The present study subjects a thermoelectric module to thermal cycling and evaluates the evolution of its thermoelectric performance through measurements of the thermoelectric figure of merit, ZT, and its individual components. The Seebeck coefficient and thermal conductivity are measured using steady-state infrared microscopy, and the electrical conductivity and ZT are evaluated using the Harman technique. These properties are tracked over many cycles until device failure after 45,000 thermal cycles. The mechanical failure of the TE module is analyzed using high-resolution infrared microscopy and scanning electron microscopy. A reduction in electrical conductivity is the primary mechanism of performance reduction and is likely associated with defects observed during cycling. The effective figure of merit is reduced by 20% through 40,000 cycles and drops by 97% at 45,000 cycles. These results quantify the effect of thermal cycling on a commercial TE module and provide insight into the packaging of a complete TE module for reliable operation.