Impact of grain size on the Seebeck coefficient of bulk polycrystalline thermoelectric materials
TL;DR: Based on the Boltzmann transport equation of electrons and taking the scattering effect of electrons in the grain boundary as the boundary conditions of electrons transport in grain, this article presented a theoretical model for the Seebeck coefficient of bulk polycrystalline thermoelectric materials, and applied it to studying the grain size effect on the seebeck coefficient, and discussed the effects of transmissivity, temperature and the mean free path of electrons on the size effect.
Abstract: Based on the Boltzmann transport equation of electrons and taking the scattering effect of electrons in the grain boundary as the boundary conditions of electrons transport in the grain, we presented a theoretical model for the Seebeck coefficient of bulk polycrystalline thermoelectric materials, and applied it to studying the grain size effect on the Seebeck coefficient. Then we discussed the effects of transmissivity, temperature and the mean free path of electrons on the size effect. The results show that the proposed theoretical model is reasonable and effective and the predicted results for the Seebeck coefficient are in good agreement with the experimental data reported in literature. The bulk polycrystalline materials have notable (big) grain size effects on the Seebeck coefficient, and the influences of transmissivity, temperature and the mean free path of electrons on the Seebeck coefficient are also significant.
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TL;DR: In this article, a grain size control method for growing nanocrystalline SnSe thin films through a glancing angle pulsed-laser deposition approach was demonstrated, which reduced the grain size of the thin film due to a shadowing effect to the adatoms.
47 citations
TL;DR: In this paper, a composite-like microstructure was designed to improve the thermoelectric (TE) properties of Bi2S3 polycrystals, where the nanorods provided good electron transport paths, and the carrier mobility was improved by more than two orders of magnitude by mixing 10 wt% nanors into the mechanical alloying (MA)-derived powders.
Abstract: We have designed a composite-like microstructure to improve the thermoelectric (TE) properties of Bi2S3 polycrystals The nanosized Bi2S3 powders derived from mechanical alloying (MA) were mixed with [001] oriented single crystalline Bi2S3 nanorods prepared by hydrothermal synthesis (HS), which were densified by spark plasma sintering (SPS) to form a composite-like microstructure bulk with road-like structures consisting of nanorods Because the nanorods provide good electron transport paths, the carrier mobility of the composite-like Bi2S3 bulk materials was improved by more than two orders of magnitude by mixing 10 wt% nanorods into the MA-derived powders The electrical resistivity was also reduced from 25 × 10−2 to 85 × 10−4 Ωm at 323 K, but the thermal conductivity was just slightly increased, resulting in a significantly enhanced ZT value, which was almost two times higher than that of the nanorod-free sample This study demonstrated the possibility to significantly enhance the ZT value of TE bulks by combining the advantages of single crystals and polycrystals via controlling the microstructure without any chemical doping
37 citations
TL;DR: In this paper, the influence of the length ratio of the thermoelements theta = L-p/(L-p + L-n) on the output power and conversion efficiency of linear-TEGs was investigated for different total lengths and heights of the TEGs.
34 citations
TL;DR: In this article, the first semiconductor or ceramic to be graded microstructurally to this extent was fabricated from ZnO with a combination of modified Spark Plasma Sintering (SPS) graphite tooling, water sintering enhancements through transient liquid phase surface transport, and strategic SPS mechanical loading.
Abstract: Functionally graded material (FGM) in terms of grain size gradation is fabricated from ZnO with a combination of modified Spark Plasma Sintering (SPS) graphite tooling, water sintering enhancements through transient liquid phase surface transport, and strategic SPS mechanical loading. The grain size gradation of the ZnO FGM spans from 180 nm grains to 1.2 micrometers in a fully dense material. This is the first semiconductor or ceramic to be graded microstructurally to this extent. Predictions of the microstructure with a Master Sintering Curve (MSC) approach were done with a series of isothermal experiments on two different FGM conditions revealing a slight offset due to a constrained mechanism. The mechanical properties were tested with Vickers micro hardness across the sample, showing a gradient in hardness from 2.6 GPa to 4.2 GPa. In addition, the thermoelectric properties of the FGM were measured and show a zT of 2 × 10−5 at 100 °C compared to uniform small- and large-grained samples of 1 × 10−6. This is an order of magnitude difference making a new path for improvements of bulk thermoelectric material.
32 citations
TL;DR: In this paper, a strong thickness dependence and anomalously large enhancement in the values of the Seebeck coefficient and electrical conductivity in Bi2Te3 films at ultralow thickness was reported.
Abstract: The present study reports a strong thickness-dependence and anomalously large enhancement in the values of the Seebeck coefficient and electrical conductivity in Bi2Te3 films at ultralow thickness. An opposite sign of the Hall coefficient (negative) and Seebeck coefficient (positive) is observed in an ultrathin Bi2Te3 film (65 nm) as compared to the normally observed identical sign in the case of Bi2Te3 thin films (520 nm). A simultaneous enhancement in the values of electrical conductivity and the Seebeck coefficient results in a giant enhancement in the value of power factor from 1.86 mW/m K2 to 18.0 mW/m K2 at 416 K, with a reduction in thickness. X-ray photoelectron spectroscopy investigation reveals the absence of any significant change in stoichiometry and chemical bonding upon reduction of thickness. Magnetoresistance vs magnetic field data show a sharp dip at the lower magnetic field values, indicating a weak antilocalization effect in the case of the ultrathin film sample suggesting the role of strong spin–orbit coupling toward the carrier filtering effect resulting in enhancement of thermoelectric properties. Observation of the large Seebeck coefficient and the power factor at lower thickness values and its relationship with spin–orbit coupling is an important result, both for practical applications and for better understanding of the thermoelectric properties.
24 citations
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TL;DR: A new era of complex thermoelectric materials is approaching because of modern synthesis and characterization techniques, particularly for nanoscale materials, and the strategies used to improve the thermopower and reduce the thermal conductivity are reviewed.
Abstract: Thermoelectric materials, which can generate electricity from waste heat or be used as solid-state Peltier coolers, could play an important role in a global sustainable energy solution. Such a development is contingent on identifying materials with higher thermoelectric efficiency than available at present, which is a challenge owing to the conflicting combination of material traits that are required. Nevertheless, because of modern synthesis and characterization techniques, particularly for nanoscale materials, a new era of complex thermoelectric materials is approaching. We review recent advances in the field, highlighting the strategies used to improve the thermopower and reduce the thermal conductivity.
8,999 citations
14 Jul 1995
TL;DR: In this article, Rowe et al. proposed a method for reducing the thermal conductivity of a thermoelectric generator by reducing the carrier concentration of the generator, which was shown to improve the generator's performance.
Abstract: Introduction, D.M. Rowe General Principles and Theoretical Considerations Thermoelectric Phenomena, D.D. Pollock Coversion Efficiency and Figure-of-Merit, H.J. Goldsmid Thermoelectric Transport Theory, C.M. Bhandari Optimization of Carrier Concentration, C.M. Bhandari and D.M. Rowe Minimizing the Thermal Conductivity, C.M. Bhandari Selective Carrier Scattering in Thermoelectric Materials, Y.I. Ravich Thermomagnetic Phenomena, H.J. Goldsmid Material Preparation Preparation of Thermoelectric Materials from Melts, A. Borshchevsky Powder Metallurgy Techniques, A.N. Scoville PIES Method of Preparing Bismuth Alloys, T. Ohta and T. Kajikawa Preparation of Thermoelectric Materials by Mechanical Alloying, B.A. Cook, J.L. Harringa, and S.H. Han Preparation of Thermoelectric Films, K. Matsubara, T. Koyanagi, K. Nagao, and K. Kishimoto Measurement of Thermoelectric Properties Calculation of Peltier Device Performance, R.J. Buist Measurements of Electrical Properties, I.A. Nishida Measurement of Thermal Properties, R. Taylor Z-Meters, H.H. Woodbury, L.M. Levinson, and S. Lewandowski Methodology for Testing Thermoelectric Materials and Devices, R.J. Buist Thermoelectric Materials Bismuth Telluride, Antimony Telluride, and Their Solid Solutions, H. Scherrer and S. Scherrer Valence Band Structure and the Thermoelectric Figure-of-Merit of (Bi1-xSbx)Te3 Crystals, M. Stordeur Lead Telluride and Its Alloys, V. Fano Properties of the General Tags System, E.A. Skrabek and D.S. Trimmer Thermoelectric Properties of Silicides, C.B. Vining Polycrystalline Iron Disilicide as a Thermoelectric Generator Material, U. Birkholz, E. Gross, and U. Stohrer Thermoelectric Properties of Anisotropic MnSi1.75 , V.K. Zaitsev Low Carrier Mobility Materials for Thermoelectric Applications, V.K. Zaitsev, S.A. Ktitorov, and M.I. Federov Semimetals as Materials for Thermoelectric Generators, M.I. Fedorov and V.K. Zaitsev Silicon Germanium, C.B. Vining Rare Earth Compounds, B.J. Beaudry and K.A. Gschneidner, Jr. Thermoelectric Properties of High-Temperature Superconductors, M. Cassart and J.-P. Issi Boron Carbides, T.L. Aselage and D. Emin Thermoelectric Properties of Metallic Materials, A.T. Burkov and M.V. Vedernikov Neutron Irradiation Damage in SiGe Alloys, J.W. Vandersande New Materials and Performance Limits for Thermoelectric Cooling, G.A. Slack Thermoelectric Generation Miniature Semiconductor Thermoelectric Devices, D.M. Rowe Commercially Available Generators, A.G. McNaughton Modular RTG Technology, R.F. Hartman Peltier Devices as Generators, G. Min and D.M. Rowe Calculations of Generator Performance, M.H. Cobble Generator Applications Terrestrial Applications of Thermoelectric Generators, W.C. Hall Space Applications, G.L. Bennett SP-100 Space Subsystems, J.F. Mondt Safety Aspects of Thermoelectrics in Space, G.L. Bennett Low-Temperature Heat Conversion, K. Matsuura and D.M. Rowe Thermoelectric Refrigeration Introduction, H.J. Goldsmid Module Design and Fabrication, R. Marlow and E. Burke Cooling Thermoelements with Superconducting Leg, M.V. Vedernikov and V.L. Kuznetsov Applications of Thermoelectric Cooling Introduction, H.J. Goldsmid Commercial Peltier Modules, K.-I. Uemura Thermoelectrically Cooled Radiation Detectors, L.I. Anatychuk Reliability of Peltier Coolers in Fiber-Optic Laser Packages, R.M. Redstall and R. Studd Laboratory Equipment, K.-I. Uemura Large-Scale Cooling: Integrated Thermoelectric Element Technology, J.G. Stockholm Medium-Scale Cooling: Thermoelectric Module Technology, J.G. Stockholm Modeling of Thermoelectric Cooling Systems, J.G. Stockholm
4,192 citations
TL;DR: In this article, the ability to achieve a simultaneous increase in the power factor and a decrease in the thermal conductivity of the same nanocomposite sample and for transport in the same direction is discussed.
Abstract: Many of the recent advances in enhancing the thermoelectric figure of merit are linked to nanoscale phenomena found both in bulk samples containing nanoscale constituents and in nanoscale samples themselves. Prior theoretical and experimental proof-of-principle studies on quantum-well superlattice and quantum-wire samples have now evolved into studies on bulk samples containing nanostructured constituents prepared by chemical or physical approaches. In this Review, nanostructural composites are shown to exhibit nanostructures and properties that show promise for thermoelectric applications, thus bringing together low-dimensional and bulk materials for thermoelectric applications. Particular emphasis is given in this Review to the ability to achieve 1) a simultaneous increase in the power factor and a decrease in the thermal conductivity in the same nanocomposite sample and for transport in the same direction and 2) lower values of the thermal conductivity in these nanocomposites as compared to alloy samples of the same chemical composition. The outlook for future research directions for nanocomposite thermoelectric materials is also discussed.
3,562 citations
TL;DR: The mean free path of electrons in metals has been studied in this paper, where the authors show that electrons follow a straight line along the path of the electron in the metal atom.
Abstract: (2001). The mean free path of electrons in metals. Advances in Physics: Vol. 50, No. 6, pp. 499-537.
2,273 citations
TL;DR: The thermoelectric materials have been investigated with the goal of maximizing electrical conductivity while minimizing thermal conductivity, which is required for good thermal performance as discussed by the authors, and the results suggest that important further improvements are on the horizon with promising applications in the computer and other high-tech industries.
Abstract: Thermoelectric materials, which have applications in refrigeration and power generation, are experiencing a surge in research activity. Many different materials are investigated with the goal of maximizing electrical conductivity while minimizing thermal conductivity, which is required for good thermoelectric performance. Only recently was a 30-year deadlock in thermoelectric performance overcome. Predictions for the new materials suggest that important further improvements are on the horizon, with promising applications in the computer and other high-tech industries.
680 citations