This paper describes the first thermoelectric devices based on the V-VI-compounds Bi/sub 2/Te/sub 3/ and (Bi,Sb)/sub 2/Te/sub 3/ which can be manufactured by means of regular thin film technology in combination with microsystem technology. Fabrication concept, material deposition for some 10-/spl mu/m-thick layers and the properties of the deposited thermoelectric materials will be reported. First device properties for Peltier-coolers and thermogenerators will be shown as well as investigations on long term and cycling stability. Data on metal/semiconductor contact resistance were extracted form device data. Device characteristics like response time for a Peltier-cooler and power output for a thermogenerator will be compared to commercial devices

The field of thermoelectricity began in the early 1800s with the discovery of the thermoelectric effect by Thomas Seebeck. Seebeck found that, when the junctions of two dissimilar materials are held at different temperatures (ΔT), a voltage (V) is generated that is proportional to ΔT. The proportionality constant is the Seebeck coeffcient or thermopower: α = −δV/ΔT. When the circuit is closed, this couple allows for direct conversion of thermal energy (heat) to electrical energy. The conversion effciency, ηTE, is related to a quantity called the fgure of merit, ZT, that is determined by three main material parameters: the thermopower α, the electrical resistivity ρ, and the thermal conductivity κ.

Superlattices consist of alternating thin layers of different materials stacked periodically.The lattice mismatch and electronic potential differences at the interfaces and resulting phononand electron interface scattering and band structure modifications can be exploited to reduce phonon heat conduction while maintaining or enhancing the electron transport.This article focuses on a range of materials used in superlattice form to improve the thermoelectric figure of merit.

Thermoelectric materials could play an increasing role for the effi cient use of energy resources and waste heat recovery in the future. The thermoelectric effi ciency of materials is described by the fi gure of merit ZT = ( S 2 σ T )/ κ ( S Seebeck coeffi cient, σ electrical conductivity, κ thermal conductivity, and T absolute temperature). In recent years, several groups worldwide have been able to experimentally prove the enhancement of the thermoelectric effi ciency by reduction of the thermal conductivity due to phonon blocking at nanostructured interfaces. This review addresses recent developments from thermoelectric model systems, e.g. nanowires, nanoscale meshes, and thermionic superlattices, up to nanograined bulk-materials. In particular, the progress of nanostructured silicon and related alloys as an emerging material in thermoelectrics is emphasized. Scalable synthesis approaches of high-performance thermoelectrics for high-temperature applications is discussed at the end. 714 Physical FunctionalityThe direct conversion of heat to electricity in thermoelectric devices is based on the Seebeck effect (named for Thomas J. Seebeck, 1821). In thermoelectric cooling devices use is made of the Peltier effect (named for Jean C. A. Peltier, 1834). [3][4][5] The thermoelectric effects were initially examined in metals. These generate only small thermovoltages of a few tens of microvolts per Kelvin. The electrical potential difference generated per degree of temperature difference is called Seebeck coeffi cient, S , or thermopower.By using semiconductors, substantially higher thermovoltages of some hundreds of μ V/K can be achieved. For thermoelectric applications, low bandgap semiconductors, with typical charge carrier concentrations in the order of 10 19 /cm 3 , are considered most suitable. Apart from a large Seebeck coeffi cient, a good thermoelectric material additionally needs to exhibit a high electrical conductivity and a low thermal conductivity to obtain a large fi gure of merit, ZT , at a certain temperature. The interdependence of these quantities has limited the ZT to values around one for the best conventional thermoelectric materials. For semiconductors and thermoelectric materials, the heat conductivity depends on both free charge carriers (holes or electrons) and phonons: κ tot = κ El + κ Ph . The phonon-based thermal conductivity κ Ph is decoupled from the electric conductivity. Thus, numerous attempts for the optimization of the thermoelectric effi ciency ZT in nanostructures are based on a reduction of the heat transport by phonons.

No abstract

No abstract

We report the room-temperature, cross-plane thermal conductivities, and longitudinal speeds of sound of multilayer films [(TiTe2)(3)(Bi2Te3)(x)(TiTe2)(3)(Sb2Te3)(y)](i) (x=1-5, y=1-5) and misfit-layer dichalcogenide films [(PbSe)(m)(TSe2)(n)](i) (T=W or Mo, m=1-5, and n=1-5) synthesized by the modulated elemental reactants method. The thermal conductivities of these nanoscale layered materials fall below the predicted minimum thermal conductivity of the component compounds: two times lower than the minimum thermal conductivity of Bi2Te3 for multilayer [(TiTe2)(3)(Bi2Te3)(x)(TiTe2)(3)(Sb2Te3)(y)](i) films and five to six times lower than the minimum thermal conductivity of PbSe for misfit-layer dichalcogenides [(PbSe)(m)(TSe2)(n)](i). We attribute the low thermal conductivities to the anisotropic bonding of the layered crystals and orientational disorder in the stacking of layered crystals along the direction perpendicular to the surface

We report on an enhanced thermoelectric figure of merit ZT=sigmaS(2)T/lambda (where sigma is electrical conductivity, S is thermopower, T is absolute temperature, and lambda is thermal conductivity) for PbTe/PbSe0.20Te0.80 superlattices (SLs) and PbTe doping SLs due to a reduction of the thermal conductivity lambda parallel to the layer planes. Despite a small decrease of the power factors sigmaS(2) due to a reduction of sigma in these superlattices, the figure of merit is higher as compared to the corresponding bulk materials and reaches maximum values in the temperature range between 400 and 570 K