DOCSLIB.ORG

Energetic Stability and Thermoelectric Property of Alkali-Metal-Encapsulated Type-I Silicon-Clathrate from First-Principles Calculation

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Energetic Stability and Thermoelectric Property of Alkali-Metal-Encapsulated Type-I Silicon-Clathrate from First-Principles Calculation Materials Transactions, Vol. 54, No. 3 (2013) pp. 276 to 285 ©2013 The Japan Institute of Metals Energetic Stability and Thermoelectric Property of Alkali-Metal-Encapsulated Type-I Silicon-Clathrate from First-Principles Calculation Kaoru Nakamura+, Susumu Yamada and Toshiharu Ohnuma Central Research Institute of Electric Power Industry, Yokosuka 240-0196, Japan Possible combinations of alkali metal guest atoms and substitutional group-13 atoms in type-I Si clathrate and their thermoelectric properties were investigated using first-principles calculations. All alkali metals could be encapsulated as the guest element into a Si46 cage, and either Al or Ga was suitable for a substitutional atom. From the formation energy, possible clathrate compositions were selected as K8Al8Si38, K8Ga8Si38,Rb8Al8Si38,Rb8Ga8Si38,Cs8Al8Si38 and Cs8Ga8Si38. The thermoelectric properties of these compositions were calculated as functions of temperature and carrier density, using the Boltzmann transport equation and the calculated band energy. The obtained dependences of the Seebeck coefficient and electrical conductivity on the carrier density were discussed from the viewpoint of band structure. The thermoelectric properties were optimized to maximize ZT for each composition by controlling the carrier density. ZT µ 0.75 was predicted as the highest ZT value for hole-doped Cs8Ga8Si38. [doi:10.2320/matertrans.MBW201204] (Received November 8, 2012; Accepted December 7, 2012; Published January 25, 2013) Keywords: thermoelectric, first-principles calculation, clathrate 1. Introduction extensively investigated for application as thermoelectric materials. In order to achieve high Seebeck coefficient, a low In recent years, reusable and clean energy generation carrier density is desirable because the Seebeck coefficient is technologies have been attracting much attention. Thermo- determined from the transport of entropy per carrier. On the electric conversion is one of the promising clean energy contrary to the Seebeck coefficient, high electrical conduc- sources because it enables the conversion of wasted heat into tivity can be achieved with high carrier density. Thus, there electric power. is a tradeoff relation between the Seebeck coefficient and In 1994, Slack proposed the concept of Phonon Glass electric conductivity, and the optimal carrier density must be Electron Crystal (PGEC).1) This hypothetical material can found to maximize ZT.10) simultaneously behave as glass for phonons and as crystal for Carrier density is frequently optimized in semiconductor carriers. Filled skutterudite and clathrate compounds are nice materials by adding a dopant. Clathrate compounds are examples of Slack’s PGEC concept. Such compounds are thought to be one of the intermetallic compounds that exhibit composed of a characteristic atomic structure. “Host atoms” a Zintl phase11) in which a guest atom supplies an electron form a cage network, and good electrical conductivity is while the substitution of an aliovalent element into a cage site exhibited because of the covalent bonding of the cage can compensate for the supplied electron. If the number of network. Cages are usually formed to encapsulate the guest and substitutional atoms is properly controlled, charge additional element, which is frequently referred to as a neutrality of the system is preserved. The carrier density of “guest atom”. The guest atom is weakly bound in the cage such an intrinsic semiconductor can thus be controlled and vibrates like an Einstein oscillator. The characteristic through adjusting the composition of guest and substitutional vibration of the guest atom can scatter the lattice vibration of atoms. Among the clathrate compounds, Ge-based clathrate the cage. This concept is referred to as “rattling”. Therefore, has been widely investigated5­9) because its localized d- cage-networked materials such as glassy materials generally electrons give it favorable thermoelectric properties. Si-based exhibit quite low thermal conductivities.1­9) clathrate, on the other hand, has not been investigated as Thermoelectric materials can generate electric power compared with the Ge-based one for use in thermoelectric through the Seebeck effect. Its conversion efficiency is applications. determined from the dimensionless figure of merit (ZT), For example, reports on the ZT of Si clathrate are quite defined as follows: limited. Kuznetsov et al. estimated the ZT of Ba8Ga16Si30 to 13) 2 be 0.87 at 870 K, and C. Candofi et al. reported that a ZT of ZT ¼ s ·T=ðke þ klÞ; ð1Þ approximately 0.2 had been achieved at 600 K for Ba8Aux- 14) where s is the Seebeck coefficient, · is electrical conductivity Si46¹x, where x = 5.59. It has not been established whether and T is temperature. ke and kl are electrical and lattice the maximum ZT of Si-based clathrate exceeds 1. Si is a thermal conductivities, respectively. Generally, ZT > 1is ubiquitous element that is cheaper than Ge and is nontoxic. regarded as a standard for actual application of thermoelectric Therefore, we believe that if a stable Si-based clathrate conversion. It is crucial to increase both the Seebeck without harmful and rare-earth element will be obtained, its coefficient and the electrical conductivity while suppressing range of applications is significant, even if it only exhibited the thermal conductivity in order to achieve high thermo- a moderate ZT. Experimental optimization of additional electric performance. PGEC materials exhibit both high elements and the carrier density would require an enormous electrical and low thermal conductivities and have been number of research trials, in general. On the other hand, a numerical method of predicting the thermoelectric properties +Corresponding author, E-mail: [email protected] of materials on the basis of theoretical calculations has been Energetic Stability and Thermoelectric Property of Alkali-Metal-Encapsulated Type-I Silicon-Clathrate from First-Principles Calculation 277 developed. If such a simulation is used to optimize the electrostatic potential at the farthest site from the dopant. This composition of the compound and estimate the maximum ZT, treatment can correct distortion of the band structure induced is would help to develop effective thermoelectric materials. by long-range interaction of an ionized dopant. ET(perfect:0) and In this study, several possible combinations of guest and ET(perfect:+1) are the total energy of the perfect cell when the substitutional atoms for the Type-I Si clathrate and their charge is neutralized and when one electron is removed, thermoelectric properties were systematically investigated respectively. The Fermi energy (¾F) in eq. (2) was measured using first-principles calculation. Alkali metals were consid- from the EVBM determined in eq. (3), and it can vary within ered as guest elements because thermoelectric properties in the band gap. Chemical potentials ®i of element i were alkali metal encapsulated Si clathrates have not been revealed calculated as per atom energy in each primitive cell. Si46 unit although their electronic structures were investigated.15) was used for the perfect cell throughout the calculation. It Reducing the number of substitutional elements is expected was confirmed that the difference in the formation energy to reduce the amount of alloy scattering of the carriers more between the unit cell and the 2 © 2 © 2 expanded supercell than using alkali earth elements for the guest elements would. was about 0.1 eV. This difference does not affect our results On the basis of the calculated thermoelectric properties, we and conclusion. will discuss the optimal composition of guest and substitu- After the structural relaxation, the detailed band structure tional atoms that maximizes ZT and whether ZT > 1 can be was further calculated using the all-electron method based on achieved for Si clathrate. the Full potential Linearized Augmented Plane Wave + Local Orbital (FLAPW+lo) approach implemented in the 20) 2. Computational Procedure WIEN2k code. Rkmax, determines the size of the basis set, was set to 7, which assures convergence of total energy to A plane-wave-basis projector augmented-wave (PAW) less than 0.01 meV/atom for Si46.A12© 12 © 12 k-point method implemented in Vienna ab initio simulation package mesh was used to sample the band energy within the (VASP) code16) was used for structural relaxation and precise Brillouin zone. The exchange-correlation functional was determination of the total energy. The exchange-correlation approximated using a GGA of Engel­Vosko formalism (EV- functional was defined using a generalized gradient approx- GGA),21) which is known to reproduce the bandgap of Si and imation (GGA) of the Perdew­Burke­Ernzerhof (PBE) is previously used for the first-principles calculation of the form.17,18) The plane-wave cutoff energy was set to 300 eV Seebeck coefficient of the Zn-substituted Ge-clathrate.22) throughout the calculation. The Monkhorst­Pack scheme19) On the basis of the band energies obtained at each k-point, was used for k-point sampling. The numerical error was the band energy was interpolated using a 6-times denser grid estimated to be 1 meV/atom for a Si46 unit cell on the basis than the original k-point mesh. The thermoelectric properties, of convergence tests of the cutoff energy and k-point mesh. including the Seebeck coefficient, electrical conductivity, A force of <10¹2 eV/¡ and a total change in energy of and electronic thermal conductivity were calculated by 10¹8 eV were selected as the convergence criteria
Load more

Recommended publications
  • Thermoelectric Properties of Sb-S System Compounds from DFT Calculations
    materials Article Thermoelectric Properties of Sb-S System Compounds from DFT Calculations Hailong Yang 1,2, Pascal Boulet 1,* and Marie-Christine Record 2 1 Campus St Jérôme, Aix-Marseille University, CNRS, Madirel, 13013 Marseille, France; [email protected] 2 Campus St Jérôme, Aix-Marseille University, University of Toulon, CNRS, IM2NP, 13013 Marseille, France; [email protected] * Correspondence: [email protected]; Tel.: +33-4135-518-10 Received: 12 August 2020; Accepted: 19 October 2020; Published: 22 October 2020 Abstract: By combining density functional theory, quantum theory of atoms in molecules and transport properties calculations, we evaluated the thermoelectric properties of Sb-S system compounds and shed light on their relationships with electronic structures. The results show that, for Sb2S3, the large density of states (DOS) variation induces a large Seebeck coefficient. Taking into account the long-range weak bonds distribution, Sb2S3 should exhibit low lattice thermal conductivity. Therefore, Sb2S3 is promising for thermoelectric applications. The insertion of Be atoms into the Sb2S3 interstitial sites demonstrates the electrical properties and Seebeck coefficient anisotropy and sheds light on the understanding of the role of quasi-one-dimensional structure in the electron transport. The large interstitial sites existing in SbS2 are at the origin of phonons anharmonicity which counteracts the thermal transport. The introduction of Zn and Ga atoms into these interstitial sites could result in an enhancement of all the thermoelectric properties. Keywords: chalcogenides; thermoelectric; DFT;QTAIM; transport properties; structure-properties relationships 1. Introduction In a preceding paper [1], we performed a chemical bonding analysis on the ternary Cu-Sb-Se system compounds and showed that the weak interactions, either in local or whole structure, played an important role in lattice thermal conductivity.
    [Show full text]
  • Arsenene and Antimonene: Two-Dimensional Materials with High Thermoelectric Figures of Merit
    Arsenene and Antimonene: Two-Dimensional Materials with High Thermoelectric Figures of Merit Item Type Article Authors Sharma, S.; Sarath Kumar, S. R.; Schwingenschlögl, Udo Citation Sharma S, Kumar S, Schwingenschlögl U (2017) Arsenene and Antimonene: Two-Dimensional Materials with High Thermoelectric Figures of Merit. Physical Review Applied 8. Available: http://dx.doi.org/10.1103/physrevapplied.8.044013. Eprint version Publisher's Version/PDF DOI 10.1103/physrevapplied.8.044013 Publisher American Physical Society (APS) Journal Physical Review Applied Rights Archived with thanks to Physical Review Applied Download date 27/09/2021 11:57:17 Link to Item http://hdl.handle.net/10754/626090 PHYSICAL REVIEW APPLIED 8, 044013 (2017) Arsenene and Antimonene: Two-Dimensional Materials with High Thermoelectric Figures of Merit S. Sharma, S. Kumar, and U. Schwingenschlögl* Physical Science and Engineering Division (PSE), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia (Received 8 April 2017; revised manuscript received 22 June 2017; published 25 October 2017) We study the thermoelectric properties of As and Sb monolayers (arsenene and antimonene) using density-functional theory and the semiclassical Boltzmann transport approach. The materials show large band gaps combined with low lattice thermal conductivities. Specifically, the small phonon frequencies and group velocities of antimonene lead to an excellent thermoelectric response at room temperature. We show that n-type doping enhances the figure of merit. DOI: 10.1103/PhysRevApplied.8.044013 I. INTRODUCTION to other two-dimensional materials, such as graphene and phosphorene. To cope with growing energy demands, alternative A series of studies has explored the electronic properties of approaches are required that can reduce the dependence arsenene and antimonene [23–32].
    [Show full text]
  • Experimental Studies of the Thermoelectric Properties of Microstructured and Nanostructured Lead Salts
    Experimental Studies of the Thermoelectric Properties of Microstructured and Nanostructured Lead Salts by Kathleen C. Barron Submitted to the Department of Mechanical Engineering A . in Partial Fulfillment of the Requirements for the Degree of - - Bachelors of Science in Mechanical Engineering MASSACHUSETTS INSTITUTE OF TECHNOLOGY at the Massachusetts Institute of Technology APR 13 2005 February 2005 >'' 1ns Vv'thlbin Rnrrrn LIBRARIES All rights reserved The author hereby grants to MIT permission to reproduce an to distribute publicly paper and electronic copies of this thesis document in whole or in part. Signatureof Author ............. .............................................................. Department of Mechanical Engineering January 14, 2005 Certified by ......... .... Gang Chen Professor of Mechanical Engineering Thesis Supervisor Accepted by . ...................................................................................... Ernest Cravalho Undergraduate Officer 1. Experimental Studies in the Thermoelectric Properties of Microstructured and Nanostructured Lead Salts by Kathleen C. Barron Submitted to the Department of Mechanical Engineering in Partial Fulfillment of the Requirements for the Degree of Bachelors of Science in Mechanical Engineering Abstract Thermoelectric devices allow for direct conversion between thermal and electrical energy. There applications, however, are severely limited by their inefficiency. A reduction in thermal conductivity of a material potentially enhances its overall thermoelectric performance
    [Show full text]
  • A Review on Thermoelectric Generators: Progress and Applications
    energies Review A Review on Thermoelectric Generators: Progress and Applications Mohamed Amine Zoui 1,2 , Saïd Bentouba 2 , John G. Stocholm 3 and Mahmoud Bourouis 4,* 1 Laboratory of Energy, Environment and Information Systems (LEESI), University of Adrar, Adrar 01000, Algeria; [email protected] 2 Laboratory of Sustainable Development and Computing (LDDI), University of Adrar, Adrar 01000, Algeria; [email protected] 3 Marvel Thermoelectrics, 11 rue Joachim du Bellay, 78540 Vernouillet, Île de France, France; [email protected] 4 Department of Mechanical Engineering, Universitat Rovira i Virgili, Av. Països Catalans No. 26, 43007 Tarragona, Spain * Correspondence: [email protected] Received: 7 June 2020; Accepted: 7 July 2020; Published: 13 July 2020 Abstract: A thermoelectric effect is a physical phenomenon consisting of the direct conversion of heat into electrical energy (Seebeck effect) or inversely from electrical current into heat (Peltier effect) without moving mechanical parts. The low efficiency of thermoelectric devices has limited their applications to certain areas, such as refrigeration, heat recovery, power generation and renewable energy. However, for specific applications like space probes, laboratory equipment and medical applications, where cost and efficiency are not as important as availability, reliability and predictability, thermoelectricity offers noteworthy potential. The challenge of making thermoelectricity a future leader in waste heat recovery and renewable energy is intensified by the integration of nanotechnology. In this review, state-of-the-art thermoelectric generators, applications and recent progress are reported. Fundamental knowledge of the thermoelectric effect, basic laws, and parameters affecting the efficiency of conventional and new thermoelectric materials are discussed. The applications of thermoelectricity are grouped into three main domains.
    [Show full text]
  • Data-Driven Review of Thermoelectric Materials: Performance and Resource Considerations † ‡ ‡ ‡ § † ‡ Michael W
    Review pubs.acs.org/cm Data-Driven Review of Thermoelectric Materials: Performance and Resource Considerations † ‡ ‡ ‡ § † ‡ Michael W. Gaultois,*, , Taylor D. Sparks,*, Christopher K. H. Borg, Ram Seshadri,*, , , ∥ ∥ William D. Bonificio, and David R. Clarke † ‡ § Department of Chemistry and Biochemistry, Materials Research Laboratory, and Materials Department, University of California, Santa Barbara, California 93106, United States ∥ School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, Massachusetts 02138, United States ABSTRACT: In this review, we describe the creation of a large database of thermoelectric materials prepared by abstracting information from over 100 publications. The database has over 18 000 data points from multiple classes of compounds, whose relevant properties have been measured at several temperatures. Appropriate visualization of the data immediately allows certain insights to be gained with regard to the property space of plausible thermoelectric materials. Of particular note is that any candidate material needs to display an electrical resistivity value that is close to 1 mΩ cm at 300 K, that is, samples should be significantly more conductive than the Mott minimum metallic conductivity. The Herfindahl−Hirschman index, a commonly accepted measure of market concentration, has been calculated from geological data (known elemental reserves) and geopolitical data (elemental production) for much of the periodic table. The visualization strategy employed here allows rapid sorting
    [Show full text]
  • Optimal Band Structure for Thermoelectrics with Realistic Scattering and Bands ✉ ✉ Junsoo Park 1 , Yi Xia 2, Vidvuds Ozoliņš 3,4 and Anubhav Jain 1
    www.nature.com/npjcompumats ARTICLE OPEN Optimal band structure for thermoelectrics with realistic scattering and bands ✉ ✉ Junsoo Park 1 , Yi Xia 2, Vidvuds Ozoliņš 3,4 and Anubhav Jain 1 Understanding how to optimize electronic band structures for thermoelectrics is a topic of long-standing interest in the community. Prior models have been limited to simplified bands and/or scattering models. In this study, we apply more rigorous scattering treatments to more realistic model band structures—upward-parabolic bands that inflect to an inverted-parabolic behavior— including cases of multiple bands. In contrast to common descriptors (e.g., quality factor and complexity factor), the degree to which multiple pockets improve thermoelectric performance is bounded by interband scattering and the relative shapes of the bands. We establish that extremely anisotropic “flat-and-dispersive” bands, although best-performing in theory, may not represent a promising design strategy in practice. Critically, we determine optimum bandwidth, dependent on temperature and lattice thermal conductivity, from perfect transport cutoffs that can in theory significantly boost zT beyond the values attainable through intrinsic band structures alone. Our analysis should be widely useful as the thermoelectric research community eyes zT >3. npj Computational Materials (2021) 7:43 ; https://doi.org/10.1038/s41524-021-00512-w 1234567890():,; INTRODUCTION using model band structures and scattering15–19, but they had one Thermoelectricity enables clean electricity generation and fluid- or more of the following limitations: (1) the bands were purely free cooling. The ultimate goal of basic thermoelectric materials parabolic or parabolic-like with infinite dispersion; (2) only a single research is to design or discover materials with high figure of isotropic band was considered; (3) models for scattering and/or merit zT, commonly expressed as: transport were based on constant lifetimes, constant mean free paths, or at best scattering proportional to the density of α2σ states (DOS).
    [Show full text]
  • 1 Thermoelectric Band Engineering: the Role of Carrier Scattering Evan
    Thermoelectric Band Engineering: The Role of Carrier Scattering Evan Witkoske, Xufeng Wang, and Mark Lundstrom Purdue University, West Lafayette, IN USA Vahid Askarpour and Jesse Maassen Dalhousie University, Halifax, Nova Scotia, CA Abstract – Complex electronic band structures, with multiple valleys or bands at the same or similar energies can be beneficial for thermoelectric performance, but the advantages can be offset by inter-valley and inter-band scattering. In this paper, we demonstrate how first-principles band structures coupled with recently developed techniques for rigorous simulation of electron-phonon scattering provide the capabilities to realistically assess the benefits and trade-offs associated with these materials. We illustrate the approach using n-type silicon as a model material and show that intervalley scattering is strong. This example shows that the convergence of valleys and bands can improve thermoelectric performance, but the magnitude of the improvement depends sensitively on the relative strengths of intra- and inter-valley electron scattering. Because anisotropy of the band structure also plays an important role, a measure of the benefit of band anisotropy in the presence of strong intervalley scattering is presented. 1. Introduction The performance of a thermoelectric device is controlled by the material figure of merit [1-4], S 2σT zT = , (1) κ e +κ L where S is the Seebeck coefficient, σ the electrical conductivity, T the absolute temperature, the electronic thermal conductivity, and the lattice thermal κ e κ L conductivity. How various material parameters affect zT is well understood (e.g. [1-4]), but parabolic energy band analyses suggest that the prospects for improving the electronic contribution to zT are limited [5].
    [Show full text]
  • Thermoelectric and Galvanomagnetic Properties of Bismuth Chalcogenide Nanostructured Hetero-Epitaxial Films
    Thermoelectric and galvanomagnetic properties of bismuth chalcogenide nanostructured hetero-epitaxial films L N Lukyanova 1, Yu A Boikov 1, V A Danilov 1, O A Usov 1, M P Volkov 1, 2 , and V A Kutasov 1 1Ioffe Physical-Technical Institute, Russian Academy of Sciences, Polytekhnicheskaya 26, 194021 St.- Petersburg, Russia 2International Laboratory of High Magnetic Fields and Low Temperatures, 53-421, Wroclaw, Poland E-mail: [email protected] Abstract Hot wall technique was used to grow block single crystal films of Bi 2Te 3 and solid solutions of Bi 0.5 Sb 1.5 Te 3 on mica (muscovite) substrates. X-ray diffraction studies demonstrated that the crystalline c- axis in the films was normal to the substrate plane. Seebeck coefficient, electrical conductivity and magnetoresistivity tensor components were measured at various orientations of magnetic and electric fields in the temperature interval 77-300 K and magnetic field up to 14 T. Scattering mechanism of charge carriers in the films were studied using temperature dependences of the degeneracy parameter and the Seebeck coefficient in terms of a many-valley model of energy spectrum. Obtained results have shown that the effective scattering parameter is considerably differed from the value specific for an acoustic scattering of charge carriers in the weakly degenerate films due to an additional scattering of charge carriers on interface and interctystallite boundaries. These features of charge carrier scattering are supposed to affect electronic transport in the films and enhance figure of merit. Keywords: bismuth-telluride-based films, transport properties, charge carrier scattering mechanism PACS: 72.15.Jf, 72.20.My, 72.20.Pa 1.
    [Show full text]
  • Radioisotope Power Systems Reference Book for Mission Designers and Planners
    https://ntrs.nasa.gov/search.jsp?R=20160001769 2019-08-31T04:26:04+00:00Z JPL Publication 15-6 Radioisotope Power Systems Reference Book for Mission Designers and Planners Radioisotope Power System Program Office Young Lee Brian Bairstow Jet Propulsion Laboratory National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology Pasadena, California September 2015 JPL Publication 15-6 Radioisotope Power Systems Reference Book for Mission Designers and Planners Radioisotope Power System Program Office Young Lee Brian Bairstow Jet Propulsion Laboratory National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology Pasadena, California September 2015 This document was generated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. It summarizes research carried out at Jet propulsion Laboratory and by Glenn Research Center. For both facilities, funding was provided by the NASA Radioisotope Power Systems (RPS) Program Office at Glenn Research Center. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not constitute or imply its endorsement by the United States Government or the Jet Propulsion Laboratory, California Institute of Technology. © 2015 California Institute of Technology. Government sponsorship acknowledged. Abstract The RPS Program’s Program Planning and Assessment (PPA) Office commissioned the Mission Analysis team to develop the Radioisotope Power Systems (RPS) Reference Book for Mission Planners and Designers to define a baseline of RPS technology capabilities with specific emphasis on performance parameters and technology readiness. The main objective of this book is to provide RPS technology information that could be utilized by future mission concept studies and concurrent engineering practices.
    [Show full text]
  • Materials Today Physics 1 (2017) 50E60
    Materials Today Physics 1 (2017) 50e60 Contents lists available at ScienceDirect Materials Today Physics journal homepage: https://www.journals.elsevier.com/ materials-today-physics New trends, strategies and opportunities in thermoelectric materials: A perspective * Weishu Liu a, , Jizhen Hu a, Shuangmeng Zhang a, Manjiao Deng a, Cheng-Gong Han a, Yong Liu a, b a Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen, Guangdong 518055, PR China b Beijing Institute of Aeronautical Materials, AECC, Beijing 100095, PR China article info abstract Article history: Thermoelectric energy conversion system has great appeal in term of its silence, simplicity and reliability Received 30 May 2017 as compared with traditional power generator and refrigerator. The past two decades witnessed a Received in revised form significantly increased academic activities and industrial interests in thermoelectric materials. One of the 2 June 2017 most important impetuses for this boost is the concept of “nano”, which could trace back to the pioneer Accepted 2 June 2017 works of Mildred S. Dresselhaus at 1990s. Although the pioneer passed away, the story about the nano Available online 10 June 2017 thermoelectric materials is still continuous. In this perspective, we will review the main mile stones along the concept of thermoelectric nanocomposites, and then discuss some new trends, strategies and opportunities. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction the dilemma, we decompose the ZT definition equation, and rewrite it into ZT ¼ (S2n)(m/k)eT by applying the relationship of Thermoelectric energy conversion system has great appeal in s ¼ nem, where e, n and m are the free charge, carrier concentration term of its silence, simplicity and reliability as compared with and carrier mobility, respectively [3].
    [Show full text]
  • Multi-Mission Radioisotope Thermoelectric Generator (MMRTG)
    National Aeronautics and Space Administration Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) Space exploration missions require safe, reliable, five decades and counting. The Apollo missions long-lived power systems to provide electricity to the moon, the Viking missions to Mars, and the and heat to spacecraft and their science instru- Pioneer, Voyager, Ulysses, Galileo, Cassini and ments. One flight-proven source of dependable New Horizons mission to Pluto and the Kuiper power is Radioisotope Power Systems (RPS). Belt all used RPS. The spectacular Voyager 1 and A type of RPS is a Radioisotope Thermoelectric 2 missions, operating on RPS power since their Generator (RTG) — a space nuclear power launches in 1977, continue to function and return system that converts heat into electricity using scientific data, with both having now reached the no moving parts. void of interstellar space. The Department of Energy (DOE), in support How RTGs Work of NASA, has developed several generations of such space nuclear power systems that RTGs work by converting heat from the natural can be used to supply electricity — and useful decay of radioisotope materials into electricity. excess heat — for a variety of space exploration RTGs consist of two major elements: a heat missions. The current RPS, called a Multi- source that contains the radioisotope fuel (mostly Mission Radioisotope Thermoelectric Generator plutonium-238), and solid-state thermocouples (MMRTG), was designed with the flexibility to that convert the plutonium’s decay heat energy to operate on planetary bodies with atmospheres, electricity. such as at Mars, as well as in the vacuum of space. An MMRTG generates about 110 watts of Conversion of heat directly into electricity is electrical power at launch, an increment of power a scientific principle discovered two centuries that can be matched with a variety of potential ago.
    [Show full text]
  • Protocols for the High Temperature Measurement of the Seebeck Coefficient in Thermoelectric Materials
    IOP PUBLISHING MEASUREMENT SCIENCE AND TECHNOLOGY Meas. Sci. Technol. 24 (2013) 085601 (12pp) doi:10.1088/0957-0233/24/8/085601 Protocols for the high temperature measurement of the Seebeck coefficient in thermoelectric materials Joshua Martin Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA E-mail: [email protected] Received 30 January 2013, in final form 10 April 2013 Published 2 July 2013 Online at stacks.iop.org/MST/24/085601 Abstract In Seebeck coefficient metrology, the present diversity in apparatus design, acquisition methodology and contact geometry has resulted in conflicting materials data that complicate the interlaboratory confirmation of reported high efficiency thermoelectric materials. To elucidate the influence of these factors in the measurement of the Seebeck coefficient at high temperature and to identify optimal metrology protocols, we measure the Seebeck coefficient as a function of contact geometry under both steady-state and transient thermal conditions of the differential method, using a custom developed apparatus capable of in situ comparative measurement. The thermal gradient formation and data acquisition methodology, under ideal conditions, have little effect on the measured Seebeck coefficient value. However, the off-axis 4-probe contact geometry, as compared to the 2-probe, results in a greater local temperature measurement error that increases with temperature. For surface temperature measurement, the dominant thermal errors arise from a parasitic heat flux that is dependent on the temperature difference between the sample and the external thermal environment, and on the various thermal resistances. Due to higher macroconstriction and contact resistance in the 4-probe arrangement, the measurement of surface temperature for this contact geometry exhibits greater error, thereby overestimating the Seebeck coefficient.
    [Show full text]