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We present experimental investigation of synthesis nanostructures of p-type Bi 0.6 Sb 1.4 Te 3 thermoelectric materials. These semiconductor materials are the best convention thermoelectric materials for use near room temperature. A new synthesis method of nanopowder using the laser ablation on high speed moving target and long laser pulse has been used and carried out in an argon atmospheric pressure. The comparison between nanoparticles obtained from hot pressing process targets and low cost cold pressing process targets have been studied. The nanostructures have been characterized by x-ray diffraction, scanning electron microscope and transmission electron microscope.

The aim of the investigation is to attempt to build-up a p-n junction by means of utilizing conventional thermoelectric materials, i.e. bulk polycrystalline p-type Bi0.45Sb1.55Te3 and n-type Bi1.6Sb0.4Te3. The fabrication used a rapid and ordinary sintering procedure. The current-voltage (I-V) characteristic curves are measured for several heating times and temperatures. The results show the feasibility of obtaining a diode-like behavior with a low leakage current at ambient temperature.

The present work is focus on thermoelectric materials synthesized by economical technique and less production time for low-cost thermoelectric module fabrication. BixSb2-xTe3 polycrystalline with x = 1.6 for n-type and x = 0.45 for p-type thermoelectric materials were synthesized using two different methods, hot pressing and cold pressing process. The thermoelectric properties were measured at room temperature. The obtained ingots were cut into pellets of 3.5 x 3.5 mm 2 in cross-section and 3.8 mm in height. Two kinds of thermoelectric modules consist of seven pairs of n-p pellets from each process were constructed on aluminum substrates with polymer layer and copper layer on the top. The performances of the two modules were evaluated with temperature difference between hot side and cold side up to 100 degC. The internal resistance of hot pressing material modules is 152 mOmega, the open circuit generated voltage is 152 mVK-1 . For cold pressing materials module, the internal resistance is 175 mOmega, the opened circuit voltage generated is 1.75 mVK-1 .The maximum output power of 70.1 mW and 71.1 mW at 100 degC in temperature difference were obtained from the hot pressing material module and the cold pressing materials module respectively

The thermoelectric opportunities of some highly conducting quasi-one dimensional (Q1D) organic crystals are studied theoretically. The electrical conductivity, Seebeck coefficient and electronic thermal conductivity are investigated as functions of crystal parameters. Obtained dependences are used to determine the optimal expected values of ZT at room temperature. The mechanism for ZT enhancement and the needed tuning of crystal parameters in order to maximize the enhancement are analyzed in detail. It is shown that due to the interference of two main electron-phonon interaction mechanisms, values as high as ZT /spl sim/ 20 are possible both in nand p-type Q1D materials. Recommendations are elaborated for the realization of such materials.

Mo/sub 6/Se/sub 8/-based Chevrel phase compounds with inserted cations into cavities are interesting as a new candidate of PGEC (Phonon Glass Electron Crystal) thermoelectric materials. From band structure calculations, the compositions including TiMo/sub 6/Se/sub 8/ have been found to be semiconductor or semimetal, and therefore are expected to have good Seebeck coefficient besides low thermal conductivity. However it had been apparent that insertion of enough cations to the cavities in Mo/sub 6/Se/sub 8/ with simple process was difficult due to secondary phase and oxide appearance. We present in this paper an estimation of the effect of two inserted cations experimentally and theoretically in order to improve thermoelectric properties of Chevrel phases. The thermoelectric properties are significantly enhanced by Cu-addition, and the dimensionless figure of merit, ZT=0.22 is estimated for nominal Cu/sub 0.3/Ti/sub 1.0/Mo/sub 6/Se/sub 8/ sample at 800/spl deg/C. It is found from band structure calculations by the self-consistent Korringa-Kohn-Rostoker (KKR) method that the Fermi level tends to shift to upper state by Cu-addition. Cu-addition can compensate a loss of Ti and control carrier concentration instead of Ti.

The electric field effect (EFE) in a coaxial cylindrical capacitor configuration was used to study the modification of transport and thermoelectric properties of the semiconductors PbTe and Bi/sub 2/Te/sub 3/ as glass coated microwires. Theoretical analysis of microwire EFE was done on the basis of Poisson equation in cylindrical geometry with corresponding boundary conditions. The radial dependences of transport characteristics have been calculated for PbTe and Bi/sub 2/Te/sub 3/ wires at positive and negative polarity of the gate voltage under the assumption that the carrier mobility is similar with the bulk material mobility. Some aspects of microwire fabrication by different methods as well as some general wire characteristics are presented. The first results of experimental measurements of wire transport properties under EFE show the increasing or decreasing of the average Seebeck coefficient in dependence of gate potential polarity in accordance with the theoretical analysis.

The electrical conductivity /spl sigma/ and Seebeck coefficient S are calculated in [111] oriented p-type PbTe/PbEuTe quantum well (QW) structures using the iterative method for solving the kinetic equations. The carrier scattering by optical and acoustical phonons is considered. The dependencies of /spl sigma/ and S vs. well width d and hole concentration p are studied. It is shown that for small d=20/spl Aring/ the energy gap between oblique L and /spl Sigma/ valleys becomes small and the Seebeck coefficient achieves large values even at very high carrier concentration of p/spl sim/10/sup 20/ cm/sup -3/. The presence of high mobility degenerate holes in the longitudinal subbands L valley leads to a small decrease of S. The obtained values of the conductivity and thermoelectric power agree well with the experimental data in the concentration range of p

During past years, considerable efforts have been spent to identify new classes of thermoelectric materials with better characteristics as compared to established thermoelectric materials. Among the most promising materials discovered, compounds with the skutterudite structure have received particular attention. In this communication, we report on the use of these advanced thermoelectric materials in a solar thermoelectric generator (STG) to be mounted on a spacecraft flying to/around Mercury. The characteristics and performance of three STG concepts, obtained from theoretical simulations, are presented in detail. The design is optimized for an operation at 0.45 AU from the Sun and to produce 400 W of electrical power. The sensitivity of the design to Sun distances between 0.30 and 1 AU is also presented. It is shown that the skutterudite-based STGs could be used advantageously as primary or auxiliary power source onboard spacecraft in near Sun missions.

The thermoelectric properties of PbTe/PbEuTe quantum wells are investigated theoretically employing a more realistic well model than it was used up to now. The carrier scattering both on optical and acoustical phonons is considered. The electrical conductivity and Seebeck coefficient are calculated using the variational method taking into account the intersubband scattering. It is found that for decreasing well widths, the electrical conductivity decreases for [100] oriented structures, and increases for [111] ones. The thermopower is higher in [100] oriented structures than in [111] ones, especially for very thin wells. The power factor is also higher in [100] wells, but the more realistic is the well model the lower is the value of power factor. So, when the dependence of effective mass on well width is taken into account, the power factor for very thin wells decreases by 14% in [100] oriented quantum wells, and by 12% in [111] ones. The power factor is calculated as a function of carrier concentration and the optimal concentrations are determined for quantum wells of different heights. The results of recent experiments are discussed.

Bulk bismuth-silica nanocomposites have been prepared via powder metallurgy to study the influence of silica inclusions on the transport properties of Bi-based materials. Bi-SiO/sub 2/ ultrafine powders were produced by an arc-plasma processing. TEM investigations revealed the presence of a nanometric silica shell around each Bi grain. The nanocomposite powders were cold pressed and sintered close to the melting temperature of bismuth. The electrical resistivity was measured from 5 K to 300 K, the thermoelectric power, the thermal conductivity and the thermoelectric figure of merit were measured from 65 K to 300 K. The transport properties of pure single crystalline and polycrystalline bismuth are compared to those of nanocomposite materials.

New materials are being investigated for thermoelectric applications. Chevrel phases have an open lattice and should have low thermal conductivity. Thus they should be interesting for thermoelectric applications. We performed band structure calculations on several selenide compounds using the Korringa-Kohn-Rostoker method. TiMo/sub 6/Se/sub 8/ is found to be semimetallic while Zn/sub 2/Mo/sub 6/Se/sub 8/ is semiconducting with an indirect gap. We estimated the effectives masses for this latter compound.

PbTe thin films were prepared by pulsed laser deposition from a Nd:YAG laser (532 nm). The films were deposited onto glass substrates. Influence of deposition temperature (80-160/spl deg/C), fluence (5-13 J/cm/sup 2/) and nominal composition of the target on the chemical composition of the films was studied. It is found that the tellurium content of the film is strongly dependent on both the laser fluence and the deposition temperature. Highly textured stoichiometric films can be obtained under suitable conditions. Preliminary transport property measurements were performed on a 200 nm thick PbTe film.

This paper is devoted to a survey of the principal studies performed on Bi-Sb thermoelectric materials over the last forty years. Bi-Sb alloys are still the best n-type materials for refrigeration at low temperatures nowadays. After a brief introduction of their physical characteristics (crystallography and band structure), the elaboration, characterization and transport properties (thermoelectric and galvanomagnetic) of the Bi-Sb alloys will be presented. The results obtained on bulk materials, in single crystalline and polycrystalline forms, and thin films will be discussed.

Thermoelectric opportunities of PbTe/Pb/sub 1-x/Eu/sub x/Te quantum well structures are investigated theoretically. The electron energetic spectrum and the Fermi level position are calculated in dependence on the quantum well width and the potential barrier height for (111) and (100) oriented structures, taking into account the multivalley character of the bulk semiconductors. The electrical conductivity and Seebeck coefficient are determined for transport along the well layers using the variational method. The carrier scattering both on optical and acoustical phonons is taken into account. It is found that for (100)-structures the conductivity decreases and Seebeck coefficient increases with the well width decreasing while for (111)-structures the latter varies weakly. The values of the thermoelectric power factor are determined and analyzed. It is shown that the values of the power factor are higher in the (100) oriented structures.

We will recall briefly the thermoelectric data on single crystals of Bi, Sb, Te, Se alloys grown by the travelling heater method. The crystalline quality of these single crystals will be characterized by X-ray topography (Synchrotron Beam). The observed dislocations are parallel to the cleavage planes with a density of 10/sup 5/ cm/sup -2/. Other defects in relationship with the growth are also observed. The composition homogeneity of the crystal is analysed by thermal probe. The quality of the single crystals permits us to perform experiments on diffusion. We recall the results for the anisotropic diffusion coefficient of selenium in bismuth telluride along the solidus line and we propose a mechanism of atomic diffusion. An important increase of the growth rate up to 40 mm per day gives materials with an excellent figure of merit (Zp=3.10/sup -3/ K/sup -1/, Zn=3.10/sup -1/ K/sup -1/).

This paper is devoted to the study of the transport properties of polycrystalline Bi/sub 86.5/Sb/sub 13.5/ alloys. Pellets of polycrystalline alloys were prepared by cold pressing and sintering of ultrafine powders. The average grain size of the bulk materials was adjusted from 0.1 /spl mu/m to 200 /spl mu/m. The influence of the microstructure and the grain size on both electrical and thermal conductivity, thermoelectric power and thermoelectric figure of merit is presented.

Carrier mobilities and densities were calculated in Bi/sub 0.96/Sb/sub 0.04/ alloy in the temperature range 78-300 K. The theoretical model takes into account the particular band structure. The non parabolicity of the conduction band and the complex carrier scattering mechanisms. The adjustable parameters are found by the least-squares method from the experimental values of the twelve galvanomagnetic coefficients in weak magnetic field and of the two components of the thermopower. Calculated values of the Hall and magnetoresistance factors of electrons show a substantial deviation from unity.

The aim of this work is multiple: first the synthesis by mechanical alloying of homogeneous Bi/sub 85/Sb/sub 15/ polycrystalline powder alloys, that have been achieved with an adequate ball to powder weight ratio (10:1), second the consolidation of the powders either by sintering or by hot extrusion in order to try to introduce a texture in the material and finally to measure the thermoelectric properties of the consolidated samples in the 77-300 K temperature range.

Recently it was shown theoretically that the thermoelectric properties of certain materials can be enhanced very much by preparing them in the form of one-dimensional conductors or quantum wires. For this it was supposed that the carrier mobility is the same both in quantum wire and in bulk material. Using the model of quasi-one-dimensional cylindrical quantum wire of finite radius with infinite potential confinement, we have calculated the mobility as a function of wire thickness. The carrier scattering both on optical and acoustical phonons is taken into account. It is found that the mobility decreases with wire thickness, decreasing from values greater than to values much smaller than the bulk one. This result changes drastically the conclusion about significant increases in the figure of merit of materials by preparing them in form of quantum wire structures.

A rapid survey of some theoretical considerations concerning the use of multiple quantum well structures (MQWS) in thermoelectricity is given as well as why bismuth can be a prospective material for the development of a new class of thermoelectric systems. Problems arising from Bi film synthesis are discussed, in relation with the preparation of Bi-based MQWS. Some experimental results are reported on pulsed laser deposited Bi films prepared in our laboratory.

It seems that the lower figure of merit for sintered n type telluride compounds is due to the selenium segregation at the grain boundaries. We present the transport properties of the Bi/sub 2/Te/sub 3/ and Sb/sub 2/Te/sub 3/ binary compounds in terms of stoichiometric deviation. We discuss these properties along the pseudo-binary phase diagram to determine the domain of existence of Bi/sub 2/Te/sub 3/-Sb/sub 2/Te/sub 3/ solid solutions. The study of the (Bi,Sb,Te) phase diagram allowed us to identify a zone where n-type materials can be obtained.

Mo/sub 6/Se/sub 8/-based Chevrel phase compounds inserted cations into those cavities are interesting as a new kind of PGEC (Phonon Glass Electron Crystal) thermoelectric materials. Ti and Zn are expected to form attractive Chevrel phase thermoelectric compounds by theoretical considerations. In our previous investigation, however, it seems to be difficult that cations insert sufficiently to cavities. In this study, an attempt to increase the amount of inserted Ti by varying preparation conditions is carried out. It is apparent that this trouble is caused by the formation of a TiSe/sub 2/ secondary phase due to preferential diffusion of Se into Ti, which consequently disturbed the reaction of Mo and Se. Proper heat process and shortening of diffusion distance are effective to distribute inserted Ti-uniformity in Chevrel phase and to decrease secondary phase. According to these analyses, the suitable condition to obtain optimum Chevrel phases, the insert mechanism of cations into the cavities, and the effect of the insertion range of Ti on thermoelectric properties are discussed.

In this paper, a lab-scale investigation of the cooling performance of a free convected thermoelectric (TE) air conditioner is reported. Two types of heat exchangers were considered: a free convected vertical, rectangular fin heat exchanger at the cold side; and a force convected skive fin heat exchanger at the hot side. A computer model developed earlier for predicting the cooling performance of free convected TE air conditioner was used in the design phase. An experimental set-up was built to study the cooling performance under various operating conditions. Seven TE modules (Tianjin Lantian model TEC1-12708) were used. The volume of the chamber was about 0.024 m/sup 3/. The effects of varying the supply voltage and airflow rate of a skive fin heat exchanger were analyzed.

A new-generation general-purpose robot gripper system which applies an artificial neural network to guide a three-finger gripper has been designed. The simulation of the core part of the whole system, i.e. optimally placing three fingers for a stable grasp using the Hopfield net, has been conducted. The results obtained show that this scheme behaves in a promising fashion. The actual computation time is usually within several seconds if implemented in an analog neural net, making the real application attractive