Showing papers on "Thermoelectric effect published in 1985"

Measurement of Seebeck coefficient using a light pulse

Abstract: A high-temperature (1900 K) Seebeck coefficient apparatus is described in which small thermal gradients are generated in a sample by light pulses transmitted via light pipes. By employing an analog subtraction circuit, the Seebeck coefficient is displayed directly on an X-Y recorder. This technique presents a convenient, accurate, and rapid method for measuring the Seebeck coefficient in highly doped semiconductors as a function of temperature. The nature of the resulting display (X-Y recording) is a valuable tool in determining validity of the data. A straight line results (i.e., a minimum of hysteresis) only if all potential experimental errors are minimized. Under these conditions, the error of measurements of the Seebeck coefficient is estimated to be less than + or - 1 percent.

The correlation between the thermoelectric properties and stoichiometry in the boron carbide phase B4C−B10.5C

Abstract: Electrical conductivity, thermoelectrical power and thermal conductivity measurements on boron carbide samples show that the electrical conductivity follows the small polaron hopping theory and that thermal conductivity occurs by phonon diffusion. The evolution of these properties with carbon content illustrates the particular role played by the 13.3 at% C compound in the phase homogeneity range B10.5C to B4C. The value of the figure of merit (0.85×10−3 K at 1250 K) proves that this particular boron carbide compound could be a very interesting candidate material for high-temperature thermoelectrical conversion.

Thermoelectric properties of lanthanum sulfide

Abstract: 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.

Thermoelectric modules, used in thermoelectric apparatus and in thermoelectric devices using such thermoelectric modules

Abstract: A thermoelectric module comprises an odd number of thermoelements (1a, 2a, 1b) connected electrically in series and disposed thermally in parallel. The electrical current flowing through a heat exchanger (9) is conducted into the module by metallic members (8a, 8b) and by first and second types of connectors (4a, 4b and 6a, 6b).

Specific heat and transport properties of UPt3

Abstract: Specific heat, resistivity, thermal conductivity and thermoelectric power measurements are reported for the normal and superconducting regimes of the heavy-fermion superconductor UPt3. A comparison is made with uranium-based spin-fluctuation and cerium-based Kondo-lattice compounds.

Preparation of γ‐LaSy (1.33<y<1.50) alloys by the pressure‐assisted reaction sintering method and their thermoelectric properties

Abstract: The pressure‐assisted reaction sintering (PARS) method was used to prepare thermoelectric elements of the γ‐phase lanthanum sesquisulfide solid solution alloys which exist over a wide homogeneity range: LaSy (1.33

Microgravity beverage can cooler

Abstract: A refrigeration apparatus for cooling containers in the microgravity conditions of outer space comprising a cooler compartment having a cold plate therein which is contoured to the shape of sidewall portions of the cans to be cooled. The cold plate is coated with a complient heat transfer medium such as metal-filled silicone rubber. When the lid of the cooler is closed, the containers are firmly engaged by the complient material, forming a good conductive heat transfer relationship. A thermoelectric generator is disposed in a separate cabinet connected to one end of the cooler and includes thermoelectric elements and a heat sink operatively associated with the cold plate within the cooler. A fan is provided in combination with the thermoelectric generator for drawing air over the heat sink thereof to dissipate heat to the surrounding environment. Suitable temperature controls are provided for turning the fan and thermoelectric elements of the generator on and off, and a safety circuit is provided to protect the device against overcurrent and excessively high temperatures in the heat sink.

Lattice thermal conductivity of small grain size PbSnTe and PbGeTe thermoelectric material

Abstract: The effect of phonon grain‐boundary scattering on the lattice thermal conductivity λL of PbSnTe and PbGeTe has been investigated theoretically as a function of grain size and doping. It is concluded that for optimally doped thermoelectric material with a mean grain size of 0.5 μm, the reductions in λL of PbSnTe and PbGeTe are 11% and 14%, respectively, compared to corresponding ‘‘single crystal’’ or large grain‐size material. This reduction in λL, which accompanies the use of very small grain‐size material, would be reflected in a significant increase in the thermoelectric figure of merit and, hence, in the conversion efficiency of generators based on lead telluride technology.

Method of obtaining optimum performance from a thermoelectric heating/cooling device

Abstract: A method of selecting optimum values for the factors H and μ in a thermoelectric heating/cooling device. A system model is formulated by relating the heat transfer characteristics of the heat exchangers on the hot and cold sides of the device to the thermoelectric properties of the TE couples. The model yields a set of governing differential equations that take into account the relative flow directions of the fluids and the position dependence of the temperatures. The equations can be solved and the solutions used in an iterative procedure to select optimum values of H and μ that will meet the specified heating or cooling requirements. In a less rigorous method, the average temperatures on the hot and cold sides of the device are used, and these temperatures are mathematically expressed by equations that normally provide results within acceptable margins of error.

Transport and magnetic measurements on UPt3

Abstract: Experiments on the normal phase of UPt3 show a large positive magnetoresistivity, almost temperature‐independent, linear in field, and a positive thermoelectric power which is not linear in temperature as T→0. The superconducting phase is characterized by a high thermal conductivity with a strong T2 term, by a coherence length smaller than the mean free path, and by lower and upper critical fields H(0)c1∼60 Oe and Hc2(0)∼26 kOe.

Temperature control device for a semiconductor laser

Abstract: A temperature control device for a semiconductor laser comprises a temperature sensitive resistor for detecting the temperature of a semiconductor laser and a Peltier element connected to the semiconductor laser and controlled, with regard to the direction of its heat transmission, in accordance with the resistance value of the temperature sensitive resistor. A single power source of a single polarity low voltage is used as a power source for the Peltier element. The current generated from the single polarity power source has its polarity changed by a bridging amplifier controlled by the resistance value of the temperature sensitive resistor and is supplied to the Peltier element.

Thermoelectric figure of merit of boron phosphide

Abstract: The thermoelectric power, thermal and electrical conductivity of boron phosphide grown by chemical vapor deposition of hydrogenated compounds were measured in the temperature range from room temperature to 1000 °C and the figure of merit of boron phosphide was evaluated. The figure of merit of 8×10−4 deg−1 was obtained at 1000 °C. This is one of the largest figures of merit at 1000 °C that have ever been obtained.

Structural, magnetic and transport properties of the spinel ferrites GaxFe1-xNiCrO4

Abstract: The authors report here on X-ray diffraction, magnetic hysteresis, resistivity and thermoelectric power measurements carried out at different temperatures for the system GexFe1-xNiCrO4(x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0), which crystallises with a spinel structure. On the basis of the site-preference energy values of the individual cations (as given by Miller, and Smit and Wijn) the cation distribution is expected to be given by (Gax3+Fe1-x3+) (Ni2+Cr3+)-O4, the Ga3+ and Fe3+ ions being on the A sites and the Ni2+ and Cr3+ ions on the B sites, thus providing a selective A-site magnetic dilution with increasing x. The saturation magnetisation measurements indicate a canting of the B-site moments with an average canting angle that increases with x. Whereas the lattice is found to contract with x, the activation energy deduced from the resistivity plots and the Seebeck coefficient is found to increase with x. For a given x the resistivity decreases with temperature (T) and for a given T it increases with x. The Seebeck coefficient is found to be independent of the temperature. These results can be explained by assuming a small-polaron hopping mechanism to be responsible for the conductivity and thermoelectric effect observed in this system.

Monolithically integrated thermoelectric controlled laser diode

Abstract: The fabrication and performance characteristics of a monolithically integrated thermoelectric controlled laser diode are described. The thermoelectric element is the n‐InP substrate. The lasers (λ∼1.51 μm InGaAsP) have threshold currents of ∼20 mA and operate kink free to >10 mW/facet. A variation of active region temperature of ± 2.5 °C has been achieved using 50 mA of thermoelectric controller current. The observed frequency tuning rate associated with this temperature shift is ∼0.5 GHz/mA. The device is useful for applications that require a high degree of frequency stability or small frequency tuning. Some potential lightwave system applications are in single‐frequency transmission systems, coherent transmission systems, optical amplifiers, resonant external cavity modulators, and injection locking.

Nottingham effect of a superconducting metal.

Abstract: The emission of electrons from a metal by a strong electric field is connected with the thermoelectric Nottingham effect, which at low temperatures heats the cathode. We have studied this effect in the state of superconductivity (niobium) where other thermal effects disappear and more precise measurements become possible. The heat produced by the emission of one electron, , is measured by a microcalorimetric method with use of a field-emitter tip. is determined by a comparison of the Nottingham heat flux with a reference heat flux produced by a calibrated electron bombardment. The experiments show that increases with field strength (3 x 10/sup 7/

Temperature optimizer control apparatus and method

Abstract: Apparatus and method for controlling compressor operation in conjunction with sensing the lowest temperature operating evaporator coil, or area serviced thereby, of a commonly-piped cooling system. A thermoelectric sensor voltage output is compared with a set-point voltage by an integrator, the output of which is applied to control the pressure for the system.

Hole transport in gallium antimonide

Abstract: The Hall coefficients R, Seebeck coefficients S, and electrical resistivities ρ of two undoped samples of p‐type GaSb were measured over the temperature ranges 20–300 K for R and ρ and 40–300 K for S. The theoretical transport coefficients R, S, and ρ were fitted in a self‐consistent way to the experimental data by adjusting the material parameters. The temperature range of the analysis (80–300 K) was found to be in the transition region between a multiellipsoidal valence band structure at low temperatures and a warped sphere structure at higher temperatures. The value deduced for the heavy hole conductivity effective mass was found to be about one third of the heavy hole density‐of‐states effective mass md1≊0.9 m0 which was used from the theory of Kolodziejczak.

Electronic transport in boron carbides

Abstract: The electronic transport of boron carbides, B1−xCx with 0.1≤x≤0.2, between 300K and 1200 K is inconsistent with conventional models of both itinerant and hopping transport. While the thermally activated conductivities and the low weakly activated Hall mobilities suggest the hopping of a high density (∼1021 cm−3) of small polarons, the spin densities are orders of magnitude smaller than this. Furthermore, the p‐type Seebeck coefficients are both large (≳100 μV/K) and strongly increasing functions of temperature, rather than being small and weakly temperature dependent as expected of degenerate semiconductors. Finally, unlike ‘‘standard’’ hopping systems, the electrical conductivity decreases with applied pressure. This is due to a pressure dependent increase of the conductivity activation energy. The anomalous thermoelectric, magnetic, and pressure‐dependent transport properties are attributed to the charge carriers being hole‐like small singlet bipolarons which hop between inequivalent B11C icosahedra.

Changes in Seebeck coefficient of Pt and Pt 10% Rh after use to 1700°C in high-purity polycrystalline alumina

Abstract: A technique is presented that enables the effects of temperature on the Seebeck coefficient to be assessed for individual wires. The technique, involving a high-resolution thermoelectric scanning rig and a nonuniform conditioning furnace of known temperature profile, was applied to 0.5-mm-diameter wires of Pt and Pt 10% Rh. Changes were observed in Seebeck coefficient when these wires were used in high-purity twin-bore insulation for up to 200 h at temperatures over the range 500 to 1700°C. Contamination from the insulation was found to be transmitted by a vaporization process, having an activation energy of 3 eV. This caused changes of up to 0.14 μV · °C−1 in Pt and 0.01 μV · °C−1 in Pt 10% Rh. Rhodium transfer to the pure Pt wire changed its Seebeck coefficient by up to 5 μV · °C−1. The consequences of both processes for thermocouple pyrometry are presented.

Thermoelectric properties of Ga1−xAlxAs

Abstract: Theoretical and experimental results describing the dependence of the Seebeck and Peltier coefficients on the composition of Ga1−xAlxAs solid solution are given. The Seebeck coefficient for nondegenerately doped n‐ and p‐type Ga1−xAlxAs is given by the simple expressions αn=(k/e)(lnNc/n+2) and αp=−(k/e)(lnNv/p+2), respectively. The dependence of α on the composition of Ga1−xAlxAs solid solutions is linear for p type and nonlinear for n type. This relation is dependent on the type of carrier that is involved in the conduction process, as well as the detailed band structure of the material. For p‐type material, two kinds of carriers are involved: heavy and light holes; for n‐type material, three kinds of carriers are involved: one direct electron and two indirect electrons. The direct electrons are dominant for Al composition of 0

Thermoelectric configuration having foreign-layer contacts

Abstract: The object of the invention is to improve the efficiency of Peltier elements and thermocouples. The solution proposed consists in designing a thermal shank from two separate and unequally annealed parts in such a way that said parts have a multiplicity of contact points with one another. Said contact points are electrical and thermal contact resistances connected in parallel and having a foreign layer. The foreign layer of the contacts is thinner than 1 . 10 cm, so that its electrical conductivity is enhanced by means of the wave-mechanical tunnel effect. The diameter of the contact points is so small that the temperature difference between the two parts of the thermal shank drops predominantly in the foreign layer. Thus the foreign layer becomes the active thermal shank of a Peltier element or thermocouple, whose efficiency is enhanced as a result of the extreme fields in the foreign layer. Figure 2 of the description is a typical illustration of the thermoelectric configuration having foreign-layer contacts 3.

Thermoelectric and thermal properties of GaAlAs Peltier-cooled laser diodes

Abstract: Analyses of heat spreading, temperature distribution, and resultant cooling effects in a monolithically Peltier‐cooled laser (MPCL) structure are presented. The analyses were obtained by using Laplace’s equation and were made under steady‐state conditions, assuming constant thermal conductivity. In this MPCL structure a metal surface layer surrounds a heat‐generating p‐n laser junction. It is shown that by depositing relatively thick metallic cooling plates a 15% temperature reduction and 25% thermal spreading can be achieved. This heat spreading due to the passive cooling is added to the cooling obtained when the Peltier cooler is operated. Experimental measurements of the effect of Peltier cooling reveal a 6.8 °C reduction in junction temperature corresponding to a wavelength shift of as much as 20 A.

Ion beam mixing to produce Bi/Sb alloys for thin film thermoelectric devices

Abstract: Ion beam mixing using 80 keV Ar+ and 120 keV Kr+ has been used to produce thin films of BiSb with various compositions of Sb ranging from 5% to 49%. In addition, n- and p-type doping of the films was attempted by the addition of Se and Sn during the mixing process. Rutherford backscattering analysis indicated that uniform composition films were formed after doses of 1.5–3 × 1016 Ar+cm−2and 7 × 1015 Kr+cm−2. TEM measurements show that grain growth occurs during the mixing. Thermo-electric measurements indicate that the Seebeck coefficient, S, has a maximum value of 66 μ V K . for an Sb concentration of 13%. This alloy also exhibits a 30% increase in the figure of merit over that of a pure Bi film. Attempts to dope the BiSb films using Sn and Se resulted in no change in S but an increase of 35% in the Seebeck voltage, Vs.

Heat sensitive tape and method of making same

Abstract: A heat sensitive tape capable of generating a temperature representative measurable voltage. The tape includes an elongated flexible strip of electrically non-conductive material. A pair of thermoelectric conductors extend along the strip in spaced apart side-by-side relation. The tape also includes an electrical insulation capable of passively self-generating a temperature representative voltage between the conductors when the tape is exposed to ambient temperature. The insulation causes a change in the temperature representative measurable voltage with an increase or decrease in temperature at every location along the strip. A change in the temperature representative measurable voltage under such condition is representative of a change in ambient temperature. The insulation also causes a change in the temperature representative measurable voltage with an increase in temperature above the prevailing ambient at any location along the strip. With this arrangement, the heat sensitive tape may be utilized not only to monitor ambient temperature, but also to monitor for any localized increase in temperature.