Thermoelectric coefficients become a function of the applied field and temperature gradient if the latter become large enough. So in analyzing device performance in this regime accurately, it is important to include the non-linear terms. Non-linearity is a consequence of electron heating. For low doping concentrations, nonlinearity can happen at low currents. We will show that at room temperature in InGaAs it starts at practical currents on the order of 105 A/cm2. At low temperatures the Peltier coefficient goes to zero. However, its nonlinear term does not change as much. Since the nonlinear heat current goes with the third power of current, there is a chance that in some cases it can overcome the joule heating. We will show that at T=77K the cooling power can be enhanced by a factor of seven compared to room temperature. Nonlinearity of the Seebeck coefficient becomes an important factor when high temperature gradients are applied on nanoscale samples, and can lead to enhanced power generation

The thermoelectric properties of Ni1-xCux (0<x<1) alloy are measured from 323K to 950K. The sample with optimized composition, Ni70Cu30 is found to possess large power factor value of 0.012 Wm−1K−2 at around 950K. Estimated figure of merit value ZT is 0.21 for Ni50Cu50 and 0.18 for Ni70Cu30 at the same temperature. A novel attempt of high-throughput parallel synthesis using multiple-wells is carried out to test the feasibility of combinatorial approach in this material system. The Seebeck coefficient is visualized over the multiple-wells combinatorial library and the other Ni-Cu composition-spread, and it is proved that further enhancement of throughput could be possible by conducting systematic experiments based on the combinatorial approaches performed in this study.

Einstein temperatures of guest atoms in Ba-Ge-(Al, In) type-III clathrate compounds have been estimated from the temperature dependence of the atomic displacement parameters determined by synchrotron X-ray powder diffractions. The lowest temperature is obtained for the vibration of Ba(2) atoms along the x-direction, which corresponds to the “rattling motion” of the guest atoms in the compounds. The temperature estimated is significantly low of about 50 K, which agrees with the fact that the compounds have small lattice thermal conductivities of about 0.6 W/mK. Though the lattice thermal conductivity of Ba24Ge88Al12 is larger than that of Ba24Ge88In12, the Einstein temperature of Ba24Ge88Al12 is slightly smaller than that of Ba24Ge88In12. This discrepancy can be explained by the consideration of higher Debye temperature of Ba24Ge88Al12 than that of Ba24Ge88In12, that is, lattice thermal conductivity without “rattling motion” is larger for Ba24Ge88Al12 than that for Ba24Ge88In12.

We report on the development of an efficient n-type skutterudite based on the double-filled structure of CoSb3. The chosen filler species Ba and Yb have a large phonon contrast and this combination is very effective in lowering the lattice thermal conductivity. The highest figure of merit in excess of 1.3 is obtained near 800K and the figure of merit greater than unity persists down to temperatures of about 550K. The compounds are synthesized with high purity Co (99.998%) and Sb (99.9999%). In order to reduce the cost of the materials, we have also prepared filled skutterudites of similar composition but using less pure Co (99.8%) and Sb (99.999%). The figure of merit of these lower purity compounds reaches ZT = 1 at 800K with the materials' cost dramatically reduced.

The compounds Mg2X (where X=Si, Ge, Sn) crystallize in the antifluorite structure. They possess properties that are similar to that of the group IV elemental semiconductors thus they have long been recognized as good candidates for thermoelectric applications. In addition, their properties can be readily tuned by doping or alloying. However, optimal performance of these materials requires continued investigation. We present low-temperature transport properties measurements of Sb doped Mg2X. Structure-property relationships are reported while their thermoelectric properties are investigated systematically in order to elucidate their potential as thermoelectric materials.

There are a variety of material systems employing different strategies in an effort to establish a new paradigm for thermoelectric materials performance. One approach is the PGEC, or “phonon-glass electron crystal”, approach were research towards optimization of the electrical properties of very low thermal conductivity materials is key. Other efforts focus on materials that exhibit high power factors via quantum-confinement or nano-scale affects. Still others focus on “engineering” metastable phases that possess properties that are distinct, if not unique, to solid state chemistry. All these approaches are valid and provide a fundamental knowledge base whereby present and future scientific materials discoveries will lead to new technological improvements. This paper focuses on bulk materials, in particular those material systems currently under investigation in the novel materials laboratory at the University of South Florida and the requirements and strategies for their optimization towards improved thermoelectric properties.

Theoretical work based on one-dimensional (1D) models indicates that Bi wires with diameter smaller than 50 nm can exhibit superior thermoelectric properties since the density of states at the Fermi level of a 1D system can be tuned to very high values. Recently, angle-resolved photoemission spectroscopy (ARPES) studies of Bi surfaces have shown that Bi nanowires support Rashba spin-orbit surface states, with high carrier densities of around 5×1012/cm−2, that have not been considered in current models of Bi nanowires. According to our estimates, the sheath of surface charge on Bi nanowires should contribute substantially to the thermopower of Bi nanowires. We carried out an experimental study of the transport properties and thermopower of bismuth nanowire arrays (NWA) with wire diameters ranging between 60 nm and 13 nm to investigate these phenomena. The Rashba interaction is a spin orbit interaction that is important for surfaces of materials consisting of heavy ion elements; thermoelectric materials frequently consist of these elements (i.e.PbTe) because they scatter phonons and form low thermal conductivity materials.

Thermoelectric elements convert a part of thermal power into electrical, developing the Seebeck effect. A number of thermoelectric elements can be connected electrically in parallel and/or in series shaping a thermoelectric generator (TEG) device. The generator efficiency, η, is determined by comparing the amount of electricity produced (PTEG) to the total amount of heat induced (QH). The possible use of such a device for the recovery of wasted heat can considerably help the world effort for energy savings and the reduction of greenhouse gases.

A measuring system and a modeling approach which takes into account the thermal contact resistances have been developed, allowing the characterization of TEG devices under various loads and temperature gradients and thus, the evaluation of material properties. The model was applied on investigating the expected gained power and efficiency, at different places of the exhaust pipe of an intermediate size car with the use of conventional thermoelectric elements. Furthermore, the reliability of a TEG module was examined and the repercussion on fuel consumption is discussed.