Showing papers on "Thermoelectric effect published in 1996"

The best thermoelectric.

Abstract: What electronic structure provides the largest figure of merit for thermoelectric materials? To answer that question, we write the electrical conductivity, thermopower, and thermal conductivity as integrals of a single function, the transport distribution. Then we derive the mathematical function for the transport distribution, which gives the largest figure of merit. A delta-shaped transport distribution is found to maximize the thermoelectric properties. This result indicates that a narrow distribution of the energy of the electrons participating in the transport process is needed for maximum thermoelectric efficiency. Some possible realizations of this idea are discussed.

Experimental study of the effect of quantum-well structures on the thermoelectric figure of merit

Abstract: Recently, it has been shown theoretically that it may be possible to increase the thermoelectric figure of merit ($Z$) of certain materials by preparing them in the form of two-dimensional quantum-well structures. Using $\mathrm{PbTe}/{\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Eu}}_{x}\mathrm{Te}$ multiple-quantum-well structures grown by molecular-beam epitaxy, we have performed thermoelectric and other transport measurements as a function of quantum-well thickness and doping. Our results are found to be consistent with theoretical predictions and indicate that an increase in $Z$ over bulk values may be possible through quantum confinement effects using quantum-well structures.

Properties of single crystalline semiconducting CoSb3

Abstract: A study of the thermoelectric properties of the skutterudite compound CoSb3 was carried out on single crystals grown by the Bridgman gradient freeze technique. p‐ and n‐type samples were obtained over a wide range of carrier concentration. Undoped As‐grown crystals show p‐type conductivity while n‐type samples were obtained by addition of Te or Pd. Samples were characterized by x‐ray diffractometry, electron microprobe analysis, and density measurements. The physical properties of CoSb3 such as linear thermal expansion coefficient, sound velocity, and Debye temperature were also determined and are presented. Seebeck coefficient, electrical resistivity, thermal conductivity, and Hall effect measurements were performed between room temperature and about 900 K. Exceptionally high Hall mobilities were obtained on p‐type samples with a maximum room‐temperature Hall mobility of 3300 cm2 V−1 s−1 at a carrier concentration of 1×1017 cm−3. The results of the transport property measurements are discussed and are in agreement with some recent predictions based on band structure calculations. The potential of CoSb3 for thermoelectric applications is evaluated.

High‐temperature thermoelectric properties of (Zn1−xAlx)O

Abstract: A mixed oxide (Zn1−x Al x )O exhibits promising thermoelectricproperties attaining a dimensionless figure of merit ZT of 0.30 at 1000 °C, which value is much superior to other oxides and quite comparable to conventional state‐of‐the‐art thermoelectricmaterials. The addition of a small amount of Al2O3 to ZnO results in a large power factor of 10–15×10−4 W/mK2, showing a marked increase in the electrical conductivity while retaining moderate thermoelectric power. A large product of the carrier mobility and density of states would be responsible for the favorable electrical properties of the present oxide. A figure of merit Z=0.24×10−3 K−1 is attained by (Zn0.98Al0.02)O at 1000 °C, even with a high thermal conductivity. A predominant proportion of the phononthermal conductivity promises a further improvement in the thermoelectric performance by selective enhancement of phonon scattering.

Effect of Quantum-Well Structures on the Thermoelectric Figure of Merit in the Si/Si1-xGex System

Abstract: The Si/Si1-xGex quantum well system is attractive for high temperature thermoelectric applications and for demonstration of proof-of-principle for enhanced thermoelectric figure of merit Z, since the interfaces and carrier densities can be well controlled in this system. We report theoretical calculations for Z in this system, based on which Si/Si1-xGex quantum-well structures were grown by molecular-beam epitaxy. Thermoelectric and other transport measurements were made, indicating that an increase in Z over bulk values is possible through quantum confinement effects in the Si/Si1-xGex quantum-well structures.

The effect of rare‐earth filling on the lattice thermal conductivity of skutterudites

Abstract: Polycrystalline samples of Ir4LaGe3Sb9, Ir4NdGe3Sb9, and Ir4SmGe3Sb9 have been made by hot isostatic pressing of powders. The lattice thermal conductivity of these filled skutterudites is markedly smaller than that of IrSb3; thus, void filling shows promise as a method for improving the thermoelectric properties of these materials. We present the lattice thermal conductivity of these filled skutterudites in an effort to quantify the impact of void filling in this structure. It is believed that the atoms ‘‘rattle’’ in the voids of the structure and therefore interact with a broad spectrum of lattice phonons, reducing their mean free paths substantially below that in the ‘‘unfilled’’ skutterudites. An additional phonon scattering mechanism is caused by phonon‐stimulated transitions between the low‐lying energy levels of the 4f electron configurations in the case of Nd3+ and Sm3+. Magnetic susceptibility and Hall‐effect measurements are also presented.

High thermoelectric figures of merit in PbTe quantum wells

Abstract: High-quality Pb1−xEuxTe/PbTe multiple quantum wells (MQWs) have been grown by molecular beam epitaxy. The measured 300K thermoelectric properties have been compared with that of the best bulk PbTe. This experimental investigation is the first detailed study of MQW structures designed to improve ZT of thermoelectric materials and has resulted in a breakthrough in the decades-long ZT ≅ 1 barrier for a room-temperature thermoelectric material. A value of Z2DT >1.2 has been achieved for these PbTe quantum wells.

Thermoelectric Properties of Homologous Compounds in the ZnO–In2O3 System

Abstract: Homologous compounds of (ZnO){sub m}In{sub 2}O{sub 3} (m = integer) with layered structures were synthesized by reaction-sintering a mixed powder of ZnO and In{sub 2}O{sub 3} at 1,823 K for 2 h in air, and their thermoelectric properties, i.e., electrical conductivity, Seebeck coefficient, and thermal conductivity, were measured at 500 to 1,100 K. Their thermoelectric figure of merit depended on the composition, and an optimum value of m apparently existed giving the largest figure of merit.

Design theory of thermoelectric modules for electrical power generation

Abstract: One of the main requirements in the design of a thermoelectric module is to determine the optimum module geometry, based upon available thermoelectric material and manufacturing technology, which meets the given application specifications. In order to assist in determining the appropriate module geometry for thermoelectric generation, its relationship to the power output and conversion efficiency is examined. A practical procedure for optimising module geometry guided by the "economic factor" is described, together with formulae and graphs which form the foundations of thermoelectric module design.

The influence of Thomson effect on the maximum power output and maximum efficiency of a thermoelectric generator

Abstract: Considering a thermoelectric generator as a heat engine cycle, the general differential equations of the temperature field inside thermoelectric elements are established by means of nonequilibrium thermodynamics. These equations are used to study the influence of heat leak, Joule’s heat, and Thomson heat on the performance of the thermoelectric generator. New expressions are derived for the power output and the efficiency of the thermoelectric generator. The maximum power output is calculated and the optimal matching condition of load is determined. The maximum efficiency is discussed by a representative numerical example. The aim of this research is to provide some novel conclusions and redress some errors existing in a related investigation.

Experimental study of the effect of quantum-well structures on the thermoelectric figure of merit

Abstract: Experimental investigations have been performed on the thermoelectric properties on the multiple-quantum-well structures of PbTe/Pb/sub 1-x/Eu/sub x/Te grown by molecular beam epitaxy. Our results are found to be consistent with theoretical predictions and indicate that an increase in Z over bulk values may be possible through quantum confinement effects using quantum-well structures.

Thermoelectric cooling module and method for manufacturing the same

Abstract: A thermoelectric cooling module, in which an electronic device is cooled due to the Peltier effect of P-type and N-type thermoelectric semiconductor elements, comprising a heat radiating section which comprises a heat radiating electrode having a fin-shaped portion for heat radiation integrally formed, a heat absorbing section comprising heat absorbing electrode contacted with the electronic device, and a thermoelectric conversion section comprising the P-type and N-type thermoelectric semiconductor elements interposed between the heat radiating electrode and the heat absorbing electrode.

High figure of merit in Ce-filled skutterudites

Abstract: New thermoelectric materials with superior transport properties at high temperatures have been discovered. These materials are part of the large family of skutterudites, a class of compounds which have shown a good potential for thermoelectric applications. The composition of these novel materials, called filled skutterudites, is derived from the skutterudite crystal structure and can be represented by the formula LnT/sub 4/Pn/sub 12/ (Ln=rare earth, Th; T=Fe, Rn, Os, Co, Rh, Ir; Pn=P, As, Sb). In these compounds, the empty octants of the skutterudite structure which are formed in the TPn/sub 3/ (/spl sim/T/sub 4/Pn/sub 12/) framework are filled with a rare earth element. Some of these compositions, based on CeFe/sub 4/Sb/sub 12/, have been prepared by a combination of melting and powder metallurgy techniques and have shown exceptional thermoelectric properties in the 350-700/spl deg/C temperature range. At room temperature, CeFe/sub 4/Sb/sub 12/ behaves as a p-type semimetal, but with a low thermal conductivity and surprisingly large Seebeck coefficient. These results are consistent with some recent band structure calculations on these compounds. Replacing Fe with Co in CeFe/sub 4/Sb/sub 12/ and increasing the Co:Fe atomic ratio resulted in an increase in the Seebeck coefficient values. The possibility of obtaining n-type conductivity filled skutterudites for Co:Fe values higher than 1:3 is currently being investigated. Measurements on bulk samples with a CeFe/sub 3.5/Co/sub 0.5/Sb/sub 12/ atomic composition and p-type conductivity resulted in dimensionless figure of merit ZT values of 1.4 at 600/spl deg/C.

Low‐temperature transport properties of the filled and unfilled IrSb3 skutterudite system

Abstract: We have measured the electrical resistivity, ρ, thermoelectric power, α, and thermal conductivity, κ, of the skutterudite material IrSb3 in a temperature range from 300 down to 4 K. It is found that the electrical resistivity and thermopower decrease monotonically as the temperature is reduced to 50–60 K. Below approximately 60 K the resistivity rises in a semiconducting manner. It appears the thermopower exhibits a large phonon drag peak at around 20 K and then falls towards zero. The thermal conductivity increases rapidly as the temperature is decreased with a maximum at around 20 K, corresponding to the peak in the thermopower. We will discuss these results and compare them to higher temperature data from G. A. Slack and V. G. Tsoukala [(IrSb3) J. Appl. Phys. 76, 1635 (1994)]. We have also measured some of the so‐called ‘‘filled skutterudites,’’ Ir4LaGe3Sb9, Ir4NdGe3Sb9 and Ir4SaGe3Sb9. The thermoelectric properties of these materials are considerably different than those of the unfilled sample. The thermopower is considerably lower and the resistivity is a factor of 2–4 times higher than the unfilled sample at room temperature. The thermal conductivity is markedly reduced by the filling, as much as a factor of 20 reduction for some of the systems.

Current control circuit for improved power application and control of thermoelectric devices

Abstract: A current control circuit for improved power application and control of thermoelectric devices to maintain the temperature of thermoelectric devices at a set point. The circuit includes at least one thermoelectric device, an inductor device, a current sensor and a switch device operatively connected in a series connection across a pair of terminals to allow current to flow therethrough when the switch device is activated to the "on" condition; a temperature sensor operatively positioned to monitor the temperature associated with the at least one thermoelectric device; a comparator device receives an input from the current sensor and provides an output to the switch device; a programmable control device receives an input from the temperature sensor and provides an output to the comparator device, the value of the output is determined by the difference between the sensed temperature of the at least one thermoelectric device and the desired set point temperature of the at least one thermoelectric device. The comparator device activates and deactivates the switch device, determined by the output of the programmable control device, to allow current to flow through the at least one thermoelectric device to achieve the set point temperature.

Microelectronic thermoelectric device and systems incorporating such device

Abstract: A method of making a microelectronic thermoelectric device comprises the steps of providing a substrate of a predetermined material, creating thermally isolated, alternating P-type and N-type semiconductor materials on the substrate, electrically connecting the P-type areas to adjacent N-type areas on opposite sides of each P-type area so that each side of a P-type area is connected to an adjacent different N-type area and leaving a free P-type end and a free N-type end, and providing an electrical lead on the free end of the P-type area and an electrical lead on the free end of said N-type area for connection to a source of electrical power. Further, a microelectronic thermoelectric device comprises a plurality of sections of semiconductor material of a first conductivity type and a plurality of sections of second conductivity type opposite to the first type. The sections are arranged to alternate from one type to the other and are thermally isolated from one another. A plurality of metal bridges are provided to interconnect each opposite end of a section to an end of an adjacent different section of opposite conductivity type. Sections of opposite conductivity type at free ends of the arrangement have metal leads attached thereto for the application of electrical energy. The sections have a predetermined height in the range of less than 1 micron to several hundreds of microns. Systems for heating or cooling are described incorporating the microelectronic thermoelectric device.

Preparation and thermoelectric properties of the skutterudite‐related phase Ru0.5Pd0.5Sb3

Abstract: A new skutterudite phase Ru(05)Pd(05)Sb3 was prepared This new phase adds to a large number of already known materials with the skutterudite structure which have shown good potential for thermoelectric applications Single phase, polycrystalline samples were prepared and characterized by x-ray analysis, electron probe microanalysis, density, sound velocity, thermal-expansion coefficient, and differential thermal analysis measurements Ru(05)Pd(05)Sb3 has a cubic lattice, space group Im3 (T(sup 5, sub h)), with a = 9298 A and decomposes at about 920 K The Seebeck coefficient, the electrical resistivity, the Hall effect, and the thermal conductivity were measured on hot-pressed samples over a wide range of temperatures Preliminary results show that Ru(05)Pd(05)Sb3 behaves as a heavily doped semiconductor with an estimated band gap of about 06 eV The lattice thermal conductivity of Ru(05)Pd(05)Sb3 is substantially lower than that of the binary isostructural compounds CoSb3 and IrSb3 The unusually low thermal conductivity might be explained by additional hole and charge transfer phonon scattering in this material The potential of this material for thermoelectric applications is discussed

Thermoelectric device with evaporating/condensing heat exchanger

Abstract: A thermoelectric heat transfer system having a thermoelectric device (30) and a heat exchanger (20) with an evaporating surface (64) and a condensing surface (140). A working fluid is sealed within the heat exchanger. The thermoelectric device includes a thermally conductive hot plate (36) and a thermally conductive cold plate (34) with thermoelectric elements disposed therebetween and the thermoelectric elements are electrically coupled in series and thermally coupled in parallel. The evaporating surface of the heat exchanger is thermally coupled with the hot plate. A fluid flow path (52) to allow working fluid in its vapor phase to flow from the evaporating surface to the condensing surface and working fluid in its liquid phase to flow from the condensing surface to the evaporating surface.

Cooling device featuring thermoelectric and diamond materials for temperature control of heat-dissipating devices

Abstract: A cooling device for lowering the temperature of a heat-dissipating device The cooling device includes a heat-conducting substrate (composed, eg, of diamond or another high thermal conductivity material) disposed in thermal contact with the heat-dissipating device During operation, heat flows from the heat-dissipating device into the heat-conducting substrate, where it is spread out over a relatively large area A thermoelectric cooling material (eg, a Bi 2 Te 3 -based film or other thermoelectric material) is placed in thermal contact with the heat-conducting substrate Application of electrical power to the thermoelectric material drives the thermoelectric material to pump heat into a second heat-conducting substrate which, in turn, is attached to a heat sink

Multi-stage electronic cooling device

Abstract: A multi-stage electronic cooling device has an electrically insulating base plate, a first thermoelectric converter portion having the Peltier effect and disposed on one surface of the electrically insulating base plate, and a second thermoelectric converter portion having the Peltier effect and disposed on another surface of the electrically insulating base plate. A through hole is formed in the electrically insulating base plate. An electrically conductive member interconnects the first thermoelectric converter portion and the second thermoelectric converter portion via an interior of the through hole. In an optional construction, the electrically conductive member is formed of an electrically conductive coating formed on the inner peripheral surface of the through hole, and the first and second thermoelectric converter portions are disposed between the electrically insulating base plate and two additional insulating base plates at opposite sides thereof

Thermoelectric properties of mesoscopic superconductors

Abstract: We develop a general framework for describing thermoelectric effects in phase-coherent superconducting structures. Formulas for the electrical conductance, thermal conductance, thermopower, and Peltier coefficient are obtained and their various symmetries discussed. Numerical results for both dirty and clean Andreev interferometers are presented. We predict that giant oscillations of the thermal conductance can occur, even when oscillations in the electrical conductance are negligibly small. Results for clean, two-dimensional systems with a single superconducting inclusion are also presented, which show that normal-state oscillations arising from quasiparticle boundary scattering are suppressed by the onset of superconductivity. In contrast, for a clean system with no normal-state boundary scattering, switching on superconductivity induces oscillations in off-diagonal thermoelectric coefficients. \textcopyright{} 1996 The American Physical Society.

Thermoelectric Devices: Solid-State Refrigerators and Electrical Generators in the Classroom

Abstract: Thermoelectric devices provide an engaging high-tech demonstration suitable for illustrating thermodynamic principles in the classroom.

A thermoelectric infrared radiation sensor with monolithically integrated amplifier stage and temperature sensor

Abstract: We report on a monolithic integrated infrared sensor system consisting of a thermopile, a sensor measuring the chip temperature and an amplifier stage fabricated in a CMOS process on SIMOX (separation by implanted oxygen) wafers. A responsivity of 209 V W−1 and a normalized detectivity D ∗ of 1.3 × 108 cm Hz 1 2 W−1 are found for thermopiles with single-crystalline p-Si/n-polysilicon thermocouples on silicon oxide/silicon nitride membranes. A first analysis of the thermal influence of the power consumed by the circuitry on the thermopile voltage indicates that the sensor performance is not deteriorated by the integrated electronic circuitry.

Electrical transport properties of epitaxial BaTiO3 thin films

Abstract: Measurements of the temperature dependent transport properties of epitaxial BaTiO3 are reported. Electrical resistivity and thermoelectric power were measured over the temperature range of 77–300 K. Room temperature resistivities of the as‐deposited, undoped films range from 105 to 108 Ω cm, while values as low as 55 Ω cm are obtained for the La‐doped films. The resistivity shows an activated temperature dependence with the measured activation energies ranging between 0.11 and 0.50 eV. The activation energy depends strongly upon the thin film carrier concentration. Thermoelectric power measurements indicate that the films are n‐type. The Seebeck coefficient for La‐doped BaTiO3 exhibits metallike behavior, with its magnitude directly proportional to temperature. Temperature dependent resistivity and thermopower measurements indicate that the carrier mobility is activated. A transport model is proposed whereby conduction occurs in the La‐doped films via hopping between localized states within a pseudogap fo...

Fabrication of thermoelectric modules and solder for such fabrication

Abstract: A thermoelectric module (10) is formed with solder joints (28, 30), the solder containing about 50 to 99 weight percent bismuth and about 50 to 1 weight percent antimony, between the thermoelectric elements (12, 14) and the connecting conductors (24, 26). Also provided is a thermoelectric module (10) having bismuth telluride elements (12, 14) coated with a conductive material (16, 18) that does not require a nickel or other diffusion barrier. Further provided are modules (10) having conductors (24, 26) with a phosphorus-nickel surface (20, 22). Methods of manufacturing and using such thermoelectric modules (10) are further provided.

Thin-film boron-doped polycrystalline silicon70%-germanium30% for thermopiles

Abstract: CMOS-compatible thermopiles can be made by using the available polysilicon layer and aluminium layer as a thermocouple. SiGe would, however, offer a better performance than silicon, mostly due to its much lower thermal conductivity, while it maintains CMOS compatibility. The figure of merit of a highly boron doped (about 10 20 atoms cm −3 ) thin-film poly-Si 70% Ge 30% layer deposited by ultra-low-pressure chemical vapour deposition (ULPCVD) is reported. The figure of merit is measured with a dedicated structure: the Seebeck coefficient is ± 75 μ V K −1 , the thermal conductivity is ± 4.8 W mK −1 and the electrical resistivity is 23 μΩ m. The figure of merit is then calculated to be z ≈ 50 × 10 −6 K −1 .