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  • 1
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    Effect of the microstructure on the thermoelectric properties of polycrystalline lanthanum chalcogenides (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Small amounts of second phase materials can have important effects on the thermoelectric properties of polycrystalline gamma-La(3-x)X4 (X-S, Te; X in the range of 0 to 1/3). Microscopic examination by SEM of hot pressed La(3-x)Te4 samples has revealed from 1-5 vol. pct of La2O2Te, an amount which is not detected by X-ray powder diffraction measurements. This amount of La2O2Te resulting from oxygen contamination can reduce the concentration of electrons by as much as 10 to 75 percent below the electron concentration calculated for single phase La(3-x)Te4 in the composition range of greatest interest. Small amounts of second phase materials can also lower the lattice thermal conductivity by scattering low frequency phonons. These results indicate that microstructural effects should be considered when electrical and thermal properties of polycrystalline materials are analyzed.
    Keywords: SOLID-STATE PHYSICS
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  • 2
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    Growth of crystals of several boron-carbon compositions by chemical vapor deposition (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Boron-carbon compounds have been deposited by the flow of carbon tetrachloride and boron trichloride, in the presence of a large excess of hydrogen, over a graphite surface maintained at 1000-1300 C. Deposits were formed on either an RF-heated disc or a tube or insert heated by a resistance furnace. Crystalline materials ranging in composition from B2C to B17C have been obtained.
    Keywords: SOLID-STATE PHYSICS
    Type: Journal of Crystal Growth (ISSN 0022-0248); 74; 210-216
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  • 3
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    Materials for thermoelectric energy conversion (1988)
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    Publication Date: 2011-08-19
    Description: The field of thermoelectric energy conversion is reviewed from both a theoretical and an experimental standpoint. The basic theory is introduced and the thermodynamic and solid state views are compared. An overview of the development of thermoelectric materials is presented with particular emphasis being placed on the most recent developments in high-temperature semiconductors. A number of possible device applications are discussed and the successful use and suitability of these devices for space power is manifest.
    Keywords: SOLID-STATE PHYSICS
    Type: Reports on Progress in Physics (ISSN 0034-4885); 51; 459-539
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  • 4
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    High-temperature thermoelectric energy conversion. II - Materials survey (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The current status of materials research for high-temperature thermoelectric energy conversion is reviewed. Two general classes of materials show promise for high temperature figure of merit (Z) values, viz, the rare-earth chalcogenides and the boron-rich borides. The electronic transport properties of the rare-earth chalcogenides are explicable on the basis of degenerate or partially degenerate n-type semiconductors. Boron and boron-rich borides exhibit p-type hopping conductivity, with detailed explanations proposed for the transport differing from compound to compound. Some discussion is presented on the reasons for the low thermal conductivities in these materials. Also, ZTs greater than one appear to have been realized at high temperature in many of these compounds.
    Keywords: SOLID-STATE PHYSICS
    Type: Energy Conversion and Management (ISSN 0196-8904); 24; 4, 19; 331-343
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  • 5
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    Computerized data acquisition and analysis for measuring thermal diffusivity (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: JPL has been leading a concentrated effort to develop improved thermoelectric materials for space applications. Thermoelectric generators are an attractive source of electrical energy for space power because of lack of moving parts and slow degradation of performance. Thermoelectric material is characterized by: Seebeck coefficient, electrical resistivity and thermal conductivity. To measure the high temperature thermal conductivity is experimentally very difficult. However, it can be calculated from the specific heat and thermal diffusivity which are easier to measure at high temperatures, especially using the flash method. Data acquisition and analysis for this experiment were automated at JPL using inexpensive microcomputer equipment. This approach is superior to tedious and less accurate manual analysis of data. It is also preferred to previously developed systems utilizing expensive minicomputers or mainframes.
    Keywords: SOLID-STATE PHYSICS
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  • 6
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    Thermoelectric properties of rare earth chalcogenides (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The rare earth chalcogenides are important thermoelectric materials due to their high melting points, self-doping capabilities, and low thermal conductivities. Lanthanum sulfides and lanthanum tellurides have been synthesized in quartz ampules, hot-pressed into samples, and measured. The n-type Seebeck coefficients, electrical resistivities, and power factors generally all increased as the temperature increased from 200 to 1000 C. The figure-of-merit for nonstoichiometric lanthanum telluride was 0.001/deg C at 1000 C, considerably higher than for silicon-germanium. Thermoelectric measurements were made for LaTe(2) and YbS(1.4), and p-type behavior was observed for these compounds from 300 to 1100 C.
    Keywords: SOLID-STATE PHYSICS
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  • 7
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    Thermoelectric properties of lanthanum sulfide (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The Seebeck coefficient, electrical resistivity, thermal conductivity, and Hall effect have been studied in gamma-phase La(3-x)S4(LaS/y/) for compositions with x in the range from 0.04 to 0.3 (y in the range from 1.35 to 1.48) in order to ascertain its suitability for high-temperature (300 to 1400 K) thermoelectric energy conversion. In this temperature and composition range the material behaves as an extrinsic semiconductor whose degenerate carrier concentration is controlled by the stoichiometric ratio of La to S. A maximum figure-of-merit (Z) of approximately 0.0005 per K at a composition x = 0.3, y = 1.48 (LaS/1.48/) was obtained.
    Keywords: SOLID-STATE PHYSICS
    Type: Journal of Applied Physics (ISSN 0021-8979); 58; 1542-154
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  • 8
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    Conduction mechanism in boron carbide (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Electrical conductivity, Seebeck-coefficient, and Hall-effect measurements have been made on single-phase boron carbides, B(1-x)C(x), in the compositional range from 0.1 to 0.2 X, and between room temperature and 1273 K. The results indicate that the predominant conduction mechanism is small-polaron hopping between carbon atoms at geometrically inequivalent sites.
    Keywords: SOLID-STATE PHYSICS
    Type: Physical Review B - Solid State, 3rd Series (ISSN 0556-2805); 29; 4582-458
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  • 9
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    Electronic transport properties of hot-pressed B6Si (1987)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Measurements of the electrical conductivity, Seebeck coefficient and Hall mobility from -300 K to -1300 K have been carried out on multiphase hotpressed samples of the nominal composition B6Si. In all samples the conductivity and the p-type Seebeck coefficient both increase smoothly with increasing temperature. By themselves, these facts suggest small-polaronic hopping between inequivalent sites. The measured Hall mobilities are always low, but vary in sign. A possible explanation is offered for this anomalous behavior.
    Keywords: SOLID-STATE PHYSICS
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  • 10
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    Effect of Ga and P dopants on the thermoelectric properties of n-type SiGe (1989)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The purpose of this study was to hot-press improved n-type Si80Ge20/GaP samples directly (without any heat treatment) and to confirm that a Ga/P ratio less than one increases the solubility of P and, hence, improves the power factor and Z. One of the three samples (Ga/P = 0.43) had an improvement in Z of about 20 percent between 400 and 1000 C over that for standard SiGe. This demonstrates that improved samples can be pressed directly and that a Ga/P ratio less than one is necessary. The other two samples (Ga/P = 0.33 and 0.50) had Z's equal to or less than that of standard SiGe but had a lower hot-pressing temperature than the improved sample.
    Keywords: SOLID-STATE PHYSICS
    Type: IECEC-89; Aug 06, 1989 - Aug 11, 1989; Washington, DC; United States
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