An Investigation Into Lead Telluride Lead Sulfide Composites and Bismuth Tin Telluride Alloys for Thermoelectric Applications PDF Download
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Author: Christopher M. Jaworski
Publisher:
ISBN:
Category : Bismuth alloys
Languages : en
Pages :
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Abstract: With the global interest in cutting back dependence on non-renewable energy sources, the field of thermoelectricity has recently seen renewed interest. Additionally, several exciting breakthroughs in both nanoscale and bulk materials have led to increased figure of merit zT. Figure of merit is a indirect measurement of a material's thermoelectric efficiency; its ability to convert a thermal heat flux to electrical power, and vice versa. Material zT has been limited to approximately 1 since the 1950's; in the past decade there have been several reports of zT>1.4. The major drawback for the development of thermoelectric devices is historically low material efficiency. However, it has been predicted that only a zT=2 is necessary to reach widespread usage of thermoelectric materials. A high zT material requires high thermopower, low electrical resistivity, and low thermal conductivity. These three material parameters are all interrelated. Therefore, recent research has focused on decoupling these parameters from each other. In this thesis, the underlying theory that is necessary for characterizing thermoelectric materials is outlined. We investigate the zT increase in the material system PbTe-PbS that was achieved through nanoprecipitation of PbS rich regions in a bulk PbTe matrix. After performing a full galvanomagnetic and thermomagnetic characterization where electrical resistivity, Seebeck, Hall, and Nernst-Ettingshausen coefficients are measured we calculate Fermi level, carrier effective mass, and scattering parameter. The introduction of the second phase of PbS in PbTe does not lower the product S2[sigma] but is reported to reduce thermal conductivity. It is this decrease in thermal conductivity that leads to a gain in zT. The second system studied is Bi2Te3:Sn. It has been reported by Kulbachinskii that Sn possibly forms a resonant level in Bi2Te3, and in this thesis, we investigate this claim further. In order to do so, we calculate a Seebeck coefficient vs. carrier density (Pisarenko relation) for Bi2Te3 and confirm it with experimental and literature data. This relation is necessary to determine if one has modified the density of states of Bi2Te3 and increased thermopower over that of a similarly doped Bi2Te3 that has a normal energy dispersion relation. In addition to the galvanomagnetic and thermomagnetic measurements, Shubnikov-de Haas (SdH) measurements are performed at 1.9K. There is conflicting literature on possible interpretations of the SdH measurements, we follow both interpretations and report the results. In summary, we conclude that by doping Bi2Te3 to higher carrier densities, we could begin to dope the lower valence band thus leading to an increase in zT.
Author: Christopher M. Jaworski
Publisher:
ISBN:
Category : Bismuth alloys
Languages : en
Pages :
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Book Description
Abstract: With the global interest in cutting back dependence on non-renewable energy sources, the field of thermoelectricity has recently seen renewed interest. Additionally, several exciting breakthroughs in both nanoscale and bulk materials have led to increased figure of merit zT. Figure of merit is a indirect measurement of a material's thermoelectric efficiency; its ability to convert a thermal heat flux to electrical power, and vice versa. Material zT has been limited to approximately 1 since the 1950's; in the past decade there have been several reports of zT>1.4. The major drawback for the development of thermoelectric devices is historically low material efficiency. However, it has been predicted that only a zT=2 is necessary to reach widespread usage of thermoelectric materials. A high zT material requires high thermopower, low electrical resistivity, and low thermal conductivity. These three material parameters are all interrelated. Therefore, recent research has focused on decoupling these parameters from each other. In this thesis, the underlying theory that is necessary for characterizing thermoelectric materials is outlined. We investigate the zT increase in the material system PbTe-PbS that was achieved through nanoprecipitation of PbS rich regions in a bulk PbTe matrix. After performing a full galvanomagnetic and thermomagnetic characterization where electrical resistivity, Seebeck, Hall, and Nernst-Ettingshausen coefficients are measured we calculate Fermi level, carrier effective mass, and scattering parameter. The introduction of the second phase of PbS in PbTe does not lower the product S2[sigma] but is reported to reduce thermal conductivity. It is this decrease in thermal conductivity that leads to a gain in zT. The second system studied is Bi2Te3:Sn. It has been reported by Kulbachinskii that Sn possibly forms a resonant level in Bi2Te3, and in this thesis, we investigate this claim further. In order to do so, we calculate a Seebeck coefficient vs. carrier density (Pisarenko relation) for Bi2Te3 and confirm it with experimental and literature data. This relation is necessary to determine if one has modified the density of states of Bi2Te3 and increased thermopower over that of a similarly doped Bi2Te3 that has a normal energy dispersion relation. In addition to the galvanomagnetic and thermomagnetic measurements, Shubnikov-de Haas (SdH) measurements are performed at 1.9K. There is conflicting literature on possible interpretations of the SdH measurements, we follow both interpretations and report the results. In summary, we conclude that by doping Bi2Te3 to higher carrier densities, we could begin to dope the lower valence band thus leading to an increase in zT.
Author: Donald Beers Evans
Publisher:
ISBN:
Category : Diffusion coatings
Languages : en
Pages : 20
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Electron microprobe study of inclusions in lead telluride thermoelectric elements.
Author: Shantanu Misra
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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The search to replace the toxic lead telluride (PbTe) alloys for thermoelectric applications in power generation has led to intensive studies of other telluride-based chalcogenide semiconductors. In this context, the binary SnTe has re-emerged over the last years as a promising candidate due to its rock-salt structure and electronic valence band structure similar to PbTe. Indium is a particularly intriguing dopant for SnTe as it leads to the appearance of a resonant level and superconductivity. Another noteworthy chalcogenide semiconductor, InTe has been recently shown to harbor promising thermoelectric properties due to its remarkably very low lattice thermal conductivity. The lack of detailed studies of its transport properties makes this compound a promising area of research in the field of thermoelectrics. In this work, we report on a detailed experimental and theoretical investigations of the transport properties of these two Te-based chalcogenides (XTe; X = Sn, In) in a wide range of temperatures (2 - 800 K). In a first part, the influence of indium on the transport properties of Sn1.03-xInxTe (0 ≤ x ≤ 40 %) is considered. The experimental results are supported by electronic band structure calculations performed using the Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA). Both experimental and theoretical results demonstrate the resonant nature of In in Sn1.03Te with an optimum doping level of 2% giving the highest thermopower value for this system. Low-temperature transport properties measurements further highlight the complex evolution of the transport properties for low In contents. Investigations performed on InTe were performed on both single-crystalline and polycrystalline samples. A large single crystal of InTe was grown by the vertical Bridgman method. The possibility to control the defect concentration in InTe was considered though the saturation annealing method, carried out on the In-rich and Te-rich side of the solidus. Comparable to the peak ZT of ~ 0.7 at 780 K achieved in single-crystalline InTe within the ab plane, a maximum ZT of ~ 0.9 at 710 K was obtained in polycrystalline InTe.
Author:
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Category : Aeronautics
Languages : en
Pages : 670
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Book Description
Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Author: Christopher M. Jaworski
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Abstract: The dimensionless thermoelectric figure of merit, zT, is used to characterize the conversion efficiency of thermoelectric materials. In this dissertation, we include experimental results on new p-type semiconducting alloys based on lead telluride that have higher zT values than historical materials. Through alloying PbTe:Tl with sulfur, we demonstrate an increase in zT over the parent material PbTe:Tl. Next, we remove the toxic element Tl from the PbTe/PbS alloy and retain the high efficiency via doping heavy valence band in PbTe, a separate mechanism than the high-zT resonant level doping achieved by the impurity Tl. We present experimental evidence relevant to the valence band structure of PbTe alloys at elevated temperature and demonstrate that these alloys remain direct gap semiconductors at temperatures relevant to automotive thermoelectric waste heat recovery (
Author: W. J. GREENERT
Publisher:
ISBN:
Category :
Languages : en
Pages : 1
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The S beck coefficient, electrical resistivity, thermal conductivity, figure of merit, generating c pacity, and m erial fficie cy were measured on 20 co erci l n-type PbTe thermoelectric elements. T e ffect on these properties of thermal cycling to simulate start-up and shut ow was determined. These mea ur ts were made to determine the variation that mig be e p cted in commercial products. The efficiency in converting heat to electricity was found to vary t o A XIMUM OF (% of the average). Therm l cycli g caus or variatio i erial efficiency than differences among individual elements. The eff c of geometrical shape on t ermoelectric performa ce was lso studied. It was conclude that, in so far a aterial efficiency is concerned, a truncated conical el nt having % less volume than a cylin rical el m t ca be substituted for the cylinder with only 7-1/2% power loss, provided the major diameter is the hot junction. (Author).
Author: Dana Ben-Ayoun
Publisher:
ISBN:
Category : Electronic books
Languages : en
Pages : 0
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The demand for energy efficiency has motivated many researchers to seek for novel methods capable of enhancing the conversion of heat to electricity. Most of the recently published methods for thermoelectric (TE) efficiency enhancement discuss on the reduction of the lattice thermal conductivity, with a minor focus on improved electronic optimization. This is attributed mainly to the fact that the electronic properties are correlated and opposing each other upon increasing the carrier concentration. It has been reported that the system of PbTe-BiTe has potentially high TE performance; this chapter is focused on a detailed investigation of the co-effect of bismuth as an effective electronic dopant and at the same time, as a second phase promoter in the PbTe matrix. (PbTe)x(BiTe)1,àíx alloys were thermoelectrically examined and the values were analyzed analytically by the general effective media (GEM) approach.
Author: Donald Michael Korn
Publisher:
ISBN:
Category : Lead telluride crystals
Languages : en
Pages : 568
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Author: Tony Knittel
Publisher:
ISBN:
Category : Lead telluride alloys
Languages : en
Pages :
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Author: Kurt Weiser
Publisher:
ISBN:
Category :
Languages : en
Pages : 13
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Doping effects and photoconductivity were studied for single crystal films of lead tin telluride (Pb(0.8)Sn(0.2)Te) grown by vapor phase epitaxy. Growth of films was carried out by an evaporation condensation process in which the alloy was evaporated from a polycrystalline source and the vapor was condensed on a barium fluoride substrate. Interesting doping effects were obtained with indium which produces a deep level in the gap with unusual properties. Extensive galvanomagnetic measurements suggest that indium enters as a self-compensating impurity and pins the Fermi level near midgap, in contrast to other Group III elements such as gallium and thallium which dope the material n-type and p-type, respectively. An investigation of the kinetics of photoconductivity revealed that around the 'device temperature' of 77 K, the recombination of excess carriers is thermally activated, but becomes approximately temperature independent below 50 K. These results and the magnitude of the photoconductive life-time lead to the surprising conclusion that contrary to prevailing opinion, Auger recombination is not the dominant recombination mechanism for samples with carrier concentration in the 1-10/10 to the 16th power cc range. (Author).
