Semiconducting crystalline materials that are poor conductors of heat are important as thermoelectric materials and for technological applications involving thermal management. In the present article neutron scattering, electrical and thermal transport, heat capacity, magnetic and acoustic measurements are reported on single crystals of three semiconductors with the type I clathrate structure: Ba8Ga16Ge30, Sr8Ga16Ge30 and Eu8Ga16Ge30. Taken together these measurements suggest specific structural features that result in a crystal with the lowest possible thermal conductivity, namely that of a glass with the same chemical composition. Weakly bound atoms that rattle within oversized atomic cages in a crystal result in a low thermal conductivity, but the present data show that both rattling atoms and tunneling states are necessary to produce a true glass-like thermal conductivity.

Nanometer-sized Bi0.90Sb0.10 has been, for the first time, prepared using a hightemperature organic solution reducing method. With the presence of proper capping and stabilizing agents, we were able to produce Bi0.90Sb0.10 nanoparticles as small as ∼12 nm. Nearly monodisperse distributions were obtained through a size-selective post treatment. Transmission electron microscope characterization reveals that the as-prepared particles have a highly crystalline single rhombohedral phase. Self-assembled patterns of Bi0.90Sb0.10 were successfully achieved upon evaporation of the solvent from the nanoparticle colloids. As a step toward possible applications of these particles in thermoelectric device structures, we have also demonstrated that we are able to control the pattern of Bi0.90Sb0.10 self-assembly from 2D to 1D by employing different solvent systems with varying ratios of polar and non-polar components.

Quasicrystals have properties associated with both crystalline and amorphous materials. These properties appear to be sensitive to both composition and annealing conditions. Therefore, it is important to investigate the influence of the microstructure on the electrical and thermal transport properties of quasicrystals. AlPdMn quasicrystal samples were prepared with various levels of Re substituted for the Mn (Al70Pd20Mn10−XReX) and then subjected to different annealing conditions. Electrical resistivity, thermopower and thermal conductivity were measured on each as grown and annealed sample over a broad range of temperature, 10 K < T < 300 K. The relationship between the electrical and thermal transport properties and microstructure will be presented and discussed.

Experimental investigation of thermoelectric properties of nanowires with diameter of about 5 nm was carried out. Chrysotile asbestos (a natural mineral) was used for a sample preparation. Its nano-sized channels were filled under pressure by melted InSb or Te. The measurements showed that temperature dependences of electrical resistance and thermopower of produced quantum wires differ considerably from corresponding dependences of bulk materials. It is possible to conclude that the results obtained are better described by Lattinger liquid model than by usual Fermi gas one.

By introducing of various equivalents of PbTe into the layered framework of CsBi4Te6, the four new compounds CsPbBi3Te6 (1), CsPb2Bi3Te7 (2), CsPb3Bi3Te8 (3) and CsPb4Bi3Te9 (4), were discovered. The compounds adopt layered structures built up of anionic slabs of progressively increasing thickness. The [PbmBi3Te5+m]- (m = 1, 2, 3, 4) slabs in the four structures can be viewed as fragments excised from the PbTe-type structures with 4-, 5-, 6- and 7-monolayers, respectively. As prepared, these materials are off-stoichiometric and n-type conductors. We present preliminary results of the crystal structures and thermoelectric properties of these materials and classify them as members of the new homologous series CsPbmBi3Te5+m (m = 1 to 4).

Sb-Zn alloys have interesting thermoelectric properties. Sb3Zn4 is a high performance ptype thermoelectric material appearing as a promising substitute for PbTe due to a higher factor of merit, ZT=1.3 at 673K [1] with the advantage of being Pb free. The preparation of the Sb3Zn4 compound is, however, not without problems. Even if some authors reported measurements on a single-phased material or single crystals [1,2], others described it as multi-phased alloy giving confused explanations for this result based on the existence of metastabilities due to strong interactions in the liquid phase [3,4].

Hence, the knowledge of a very trustful phase diagram of the Sb-Zn sytem is indispensable. As the previous published data on this system were discordant, we have reinvestigated it and from our results we have elaborated and characterised the thermoelectric compound Sb3Zn4.

We have developed an instrument which simultaneously measures the thermal conductivity κ, Seebeck coefficient α, and electrical resistivity ρ of a sample, thereby determining the thermoelectric figure of merit Z = α2/(κρ). A Quantum Design Physical Property Measurement System (PPMS) provides the temperature control from 1.9 - 390 K and applied magnetic fields of up to 14 tesla. Two small probes mounted along the sample each contain thin film Cernox chip thermometers as well as electrical contacts to monitor the temperature and voltage drops across the sample. A third probe attached to the end of the sample provides a heater and current source to stimulate the sample both thermally and electrically. The sample's response to cyclic heat pulses is analyzed in real time using DSP techniques. A nonlinear least-squares fit is used, employing a two time-constant model to determine both the thermal conductivity and the Seebeck coefficient for the material. Data acquisition using these ac techniques are expedited since we can sweep both temperature and field during a measurement. Adaptive algorithms continually adjust the thermal and electrical stimuli applied to the sample, optimizing the speed and accuracy of the measurement. We present results from some of the materials measured so far, including thermal conductivity standards and Pb in the superconducting state.

We present here a thermoelectric transport property study of Bi1−xSbx alloy nanowires embedded in a dielectric matrix. Temperature-dependent resistance measurements exhibit nonmonotonic trends as the antimony mole fraction (x) increases, and a theoretical model is presented to explain the features that are related to the unusual band structure of Bi1−xSbx systems. Seebeck coefficient measurements are performed on nanowires with different diameters and compositions, showing enhanced thermopower over bulk Bi. The magneto-Seebeck coefficient of these nanowires also exhibits an unusual field dependence that is absent in bulk samples.

In this paper, a set of methods is developed to measure the Seebeck coefficient, electrical conductivity, and thermal conductivity in the cross-plane direction of thin films. The method employs microfabricated heaters, voltage and temperature sensors, and phase-lock amplifiers to determine the temperature and Seebeck voltage oscillation in the cross-plane direction of the samples, from which the thermal conductivity and Seebeck coefficient of thin films are determined simultaneously. The cross-plane electrical conductivity is also measured by a modified transmission line model. These methods are applied to Si/Ge superlattices grown by molecular beam epitaxy.

Perovskite oxide Cd3TeO6 was electron-doped by the introduction of oxygen vacancies and substitution of trivalent cations, In3+, La3+ and Bi3+. Their electric properties were investigated and compared with that of undoped Cd3TeO6. Negative temperature dependence of resistivity was observed in undoped, air-sintered Cd3TeO6. The resis tivity of Cd3−xAxTeO6 (A = In3+, La3+ and Bi3+) showed a metallic behavior with very slight temperature dependence. Indium-doped samples gave a low resistivity, which were decreased by more than three orders of magnitudes than that of air-sintered, undoped Cd3TeO6. The negative Seebeck coefficient and Hall coefficient obtained from all samples indicate that electrons are the charge carriers. The absolute Seebeck coefficients values of doped samples are decreased by 5 ∼ 10 times than that observed in undoped Cd3TeO6. Fortunately, the resistivity of indium-doped samples is low enough to provide a good thermoelectric power factor, and the optimum value of Cd2.97In0.03TeO6 was calculated as 1.35×10−4 Wm−1K−2. This result is close to that of the current best n-type perovskite thermoelectric material Ba0.4Sr0.6PbO3.

Polycrystalline metal borides AlMgB14, CaB6, and MB2 (M: transition metals) were synthesized and their thermoelectric properties were examined. Single phase of orthorhombic AlMgB14, which contains B12 icosahedral clusters as building blocks, was obtained at sintering temperatures between 1573 K and 1823 K. Seebeck coefficient (α) and electrical conductivity (σ) of the phase were about 500 (μV/K) and 10−1 (1/Ωm) at room temperature, respectively. These values are comparable to those of metal-doped β- rhombohedral boron. Synthesized AlB2-type diborides (MB2; M=Ti, V, Cr, and Mn) exhibited metallic conduction. The MB2's α varied with number of valence electrons, and showed a maximum α in VB2. The variation was similar to that predicted for pseudogap system. The CaB6 also possessed metallic conduction, but the α of the phase was as large as 200 (μV/K) with negative sign.

New thermoelectric bulk materials such as CsBi4Te6 have shown superior properties to traditional materials, however, optimal performance requires continuing investigations of doping and alloying trends. A recently modified high throughput measurement system is presented for doping and alloying investigations in several new thermoelectric materials. The modification includes a four-probe configuration for more accurate measurements while maintaining a relatively short sample preparation time. The system is fully computer controlled and provides flexible contacts to accommodate various sample dimensions. Optimal compositions are then identified for further investigations in thermoelectric prototype modules. The most promising materials will be further characterized for electrical conductivity, thermoelectric power, thermal conductivity, and Hall effect measurements as a function of temperature.

Nanowires made of thermoelectric-relevant materials were grown by electrochemical deposition. Their diameter and ordering are dictated by the porous alumina template that is fabricated on the working electrode prior to the deposition. The composition of the nanowires is controlled by the composition of the electrolyte and the deposition potential. This technique offers unique opportunities regarding the range of geometries and materials that can be employed. The structural and transport properties of these wires will be presented, and comparison will be made to nanowires synthesized by other techniques.

An object-oriented, discrete state method for simulating coupled systems was defined. A proof-of-principle simulation of the effect of acoustic phonon scattering on electrical current was performed. Steady-state and relaxation processes were numerically simulated. A relaxation time constant was measured. The numerical simulation of Peltier cooling and heating was defined as a special case of the scattering and transport physics of the proof-of-principle simulation. The scattering terms were designed to account for local interface conditions.

The thermoelectric properties of misfit cobaltites have been investigated. Their crystallographic structure consists in the stacking of layers of tilted CoO6 edge-shared octahedra, separated by rock-salt type layers. The Tl based family was first investigated : it is shown that by increasing the Tl content, the resistivity ρ can be reduced while keeping a large thermopower S. Another way to improve the figure of merit Z=S2/(ρκ) is to partially substitute Bi for Tl to increase S and keep a small ρ. A new family of Pb-based misfits has also been investigated. Two different techniques have been attempted to decrease ρ and/or increase S in this family : the partial substitution of Cu for Co, and the partial substitution of Ca for Sr.

In an effort to expand the range of operation for highly efficient, segmented thermoelectric unicouples currently being developed at the Jet Propulsion Laboratory (JPL), skutterudite phosphides are being investigated as potential high temperature segments to supplement antimonide segments that limit the use of these unicouples at a hot-side temperature of about 873-973 K. We report here on the synthesis and transport properties of one of these phosphide skutterudite materials, CoP3. Large amounts of cobalt triphosphide have been prepared by direct reaction from stochiometric powders at synthesis temperatures ranging from 873 to 1223 K. The synthesized powders were analyzed by x-ray diffractometry and hot pressed at 1273 K. The samples were analyzed by microprobe analysis and electrical conductivity, Seebeck voltage and thermal conductivity measurements were performed. The thermoelectric properties are presented and discussed as a function of temperature up to 1000 K. Initial thermal stability results are presented to assess the potential of this material for high temperature operation.

This paper reports an overview of the current state in our research program started in 1995 in collaboration with industries. This program has been aimed at making sure of the feasibility of a thermoelectric convertor for waste heat recovery of gasoline engine vehicle. Major results obtained include: (1) updated ZT-values for Pd,Pt-doped CoSb3 and partially Yb-filled skutterudite antimonides YbyM4Sb12 (M=Co, Fe, Ni; 0<y<1), (2) the performance of thermoelectric convertor using a segmented module of the skutterudites and Bi2Te3-based alloys, (3) a preliminary test of a thermoelectric stack which is the united device of thermoelectric modules and heat exchanger, when properly installed in a 2000cc class automobile.

The processing of electronic materials and devices is an important field of application of thermodynamics. Many growth processes of semi-conductors involve vapour-solid or liquid-solid interfaces which can be considered close to the thermodynamic equilibrium. Performance enhancement of thermoelectric modules can be obtained by a good knowledge of the constitution of the materials involved in their fabrication. Its requires a relevant thermodynamic analysis of the material.Making these optimized thermoelectric materials require at least three elements being thermoelectric materials typically multicomponent systems which are usually studied by a CALPHAD analysis of the relevant systems. All these problems are related to the thermodynamic quantities of species involved in the materials such as activities and free energy functions of electrons, holes and components.

In this paper we present a contribution to a better understanding of antimony based thermoelectric materials by a CALPHAD approach.

Previous models on low-dimensional thermoelectric investigation deal with the quasi twodimensional electron transport due to quantum confinement effect. The formation of sub-bands in quantum well requires that electron wave reflections or transmissions at the interface are strictly in the specular direction and the superimposed wave function keeps phase coherence. However, due to the interface non-ideality or roughness, electrons can lose coherence such that their transport will deviate from that described by two-dimensional quantum well limit theories. In this paper, we report a theoretical approach to investigate the classical size effect on in-plane thermoelectric transport at low dimensions. A theoretical model based on Boltzmann equation is established with interface scattering treated as partial specular and partial diffuse scattering boundary condition. With the infinite quantum well assumption, the classical size effect in the quantum-classical mixed regime is quantitatively demonstrated. Factors that affecting classical size effect, such as quantum well width and relaxation length, are discussed.

The possibility of a prototype thermoelectric cooling device for operation near liquid nitrogen temperatures has been explored. In these devices, the figure of merit involves a combination of the properties of the two branches of the module. Here, we investigate the fabrication of a module with a new low temperature material, CsBi4Te6 (p-type), and the best known low temperature n-type materials Bi85Sb15. Transport measurements for each of these materials show high performance at low temperatures. Known values for the figure of merit Zmax of CsBi4Te6 is 3.5 × 10−3 K−1 at 225K and for Bi85Sb15 is 6.5 × 10−3 K−1 at 77K. At 100K these values drop to 2.0×10−3 K−1 for CsBi4Te6 and 6.0×10−3 K−1 for Bi85Sb15. Theoretical simulations based on these data show a cooling of δT = 12K at 100K, which is almost three times the efficiency of a Bi2Te3 module at that temperature. We present transport measurements of elements used in the fabrication of a low temperature thermoelectric module and properties of the resulting module.