We investigated the thermoelectric voltage (TEV) of atomic contacts of nickel (Ni) by using a scanning tunneling microscope. The TEV of nanoscale junctions show fluctuation in stepwise manner. Histogram analysis of TEV observed in the Ni point contact with the conductance of 1.2 G0 (G0 = 2e2/h is the quantum of charge conductance) revealed multiple voltage peaks at larger and smaller values observed at conductance of 2.5 G0, which showed a single sharp voltage peak. Fluctuation observed in our results suggest that there is transition of the transport channel distribution caused by the thermal motion of Ni atoms.

This study demonstrates the feasibility of introducing a TaN thin film as a copper diffusion barrier for p-type (BiSb)2Te3 thermoelectric material. Compared to conventional Ni diffusion barrier, remarkably little void generation in Cu bulk or near Cu/TaN interface originated from Cu penetration is observed for TaN barrier after suffering the thermal budget of close to soldering. Diffusion behaviors of the barriers were analyzed by transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS) to make a deep understanding in clarifying interface diffusion effects among the Cu electrode, the barrier layer, and the (BiSb)2Te3thermoelectric layer.

As thermoelectric (TE) element length decreases, the impact of contact resistance on TE device performance grows more significant. In fact, for a TE device containing 100-μm tall Bi2Te3TE elements, the figure of merit ratio (ZTDevice/ZTMaterial) drops from 0.9 to 0.5 as the contact resistivity increases from 5 x 10-07 to 5 x 10-06 Ω-cm2. To understand the effects of contact resistance on bulk TE device performance, a reliable experimental measurement method is needed. There are many popular methods to extract contact resistance such as Transmission Line Measurements (TLM) and Kelvin Cross Bridge Resistor method (KCBR), but they are only well-suited for measuring metal contacts on thin films and do not necessarily translate to measuring contact resistance on bulk thermoelectric materials. The authors present a new measurement technique that precisely measures contact resistance (on the order of 5 x 10-07 Ω-cm2) on bulk thermoelectric materials by processing stacks of bulk, metal-coated TE wafers using TE industry standard processes. One advantage of this technique is that it exploits realistic TE device manufacturing techniques and results in an almost device-like structure, therefore representing a realistic value for electrical contact resistance in a bulk TE device. Contact resistance measurements for metal contacts to n- and p-type Bi2Te3 alloys are presented and an estimate of the accuracy of the measurements is discussed.

Thermoelectric materials with stable mechanical and chemical properties at high temperature are required for power generation applications. For example, gas temperatures up to 1000°C are normally present in the waste stream of industrial processes and this can be used for electricity generation. There are few semiconductor materials that can operate effectively at these high temperatures. One solution may be the use of wide bandgap materials, and in particular GaN-based materials, which may offer a traditional semiconductor solution for high temperatures thermoelectric power generation. In particular, the ability to both grow GaN-based materials and fabricate them into devices is well understood if their thermoelectric properties are favorable. To investigate the possibility of using III-Nitride and its alloys for thermoelectric applications, we synthesized and characterized room temperature thermoelectric properties of metal organic chemical vapor deposition grown GaN and InGaN with different carrier concentrations and indium compositions. The promising value of Seebeck coefficients and power factors of Si-doped GaN and InGaN indicated that these materials are suitable for thermoelectric applications.

The output power-density and the efficiency of thermo-tunnel devices are examinedas a function of inter-electrode separation, electrode work-function, and temperature. We find that these physical parameters dramatically influence the device characteristics, and under optimal conditions a thermo-tunnel device is capable of delivering a very high output power-density of ∼ 103Wcm−2. In addition, at higher temperatures, the heat-conversion efficiency of the thermo-tunnel device approaches ∼ 10%, comparable to that of a thermoelectric generator. We therefore propose that thermo-tunnel devices are promising for solid-state thermal energy conversion.

The thermoelectric properties of Mg2Si coatings prepared by Atmospheric Plasma Spray (APS), and Vacuum Plasma Spray (VPS) are presented. Seebeck coefficient results of both APS and VPS have been reported. XRD and SEM analysis of the samples are also presented to understand how microstructure influences the coating thermoelectric properties. The results suggest significant improvements can be made on the reduction of impurity including oxidation and pure silicon by using proper spray method and parameters. Thermal spray has been demonstrated before to be effective way to reduce thermal conductivity which may due to the coating microstructure. VPS result shows higher Seebeck coefficient than APS which may due to lower level of oxidization.

Owing to energy conservation of waste heat, Lead telluride, PbTe, based materials have promising good thermoelectric properties around a range of middle temperature (Fig. 1, from 300 to 600°C), due to their high melting point, fine chemical stability, and the high figure of merit Z. The general physical properties and factors affecting the figure of merit have been reviewed. This research is focused on the n-type of PbTe materials and collocated with analysis of densities, hardness, elastic modulus, and thermoelectric properties thermoelectric figure of merit ZT=GS2T/κ (where G is electrical conductivity, S is Seebeck coefficient , T is absolute temperature, and κ is thermal conductivity). Room temperature hardness and Young’s modulus are measured by nano-indentation. In this study, the hot-press compacts under the pressure of 4 ton/cm2 can reach the maximum density about 8.2 g/cm3, and hardness and elastic modulus are 0.6 GPa and 70 GPa, respectively. The figure of merit value (ZT) of PbTe in low temperature (around 340°C) was found about 1 with carrier concentration above 1019 cm−3. These results also indicate that the powder metallurgy parameters provide potentialities for further increase of the high efficiency of energy conversion in PbTe materials.

Thermoelectric power generation has been attracting attention as a technology for waste heat utilization in which thermal energy is directly converted into electric energy. It is well known that layered cobalt oxide compounds such as NaCo2O4 and Ca3Co4O9 have high thermoelectric properties in p-type oxide semiconductors. However, in most cases, the thermoelectric properties in n-type oxide materials are not as high. Therefore, n-type magnesium silicide (Mg2Si) has been studied as an alternative due to its non-toxicity, environmental friendliness, lightweight property, and comparative abundance compared with other TE systems. In this study, we fabricated π-structure thermoelectric power generation devices using p-type NaCo2O4 elements and n-type Mg2Si elements. The p- and n-type sintering bodies were fabricated by spark plasma sintering (SPS). To reduce the resistance at the interface between elements and electrodes, we processed the surface of the elements before fabricating the devices. The end face of a Mg2Si element was covered with Ni by SPS and that of a NaCo2O4 element was coated with Ag by silver paste and soldering.

The thermoelectric device consisted of 18 pairs of p-type and n-type legs connected with Ag electrodes. The cross-sectional and thickness dimensions of the p-type elements were 3.0 mm × 5.0 mm × 7.6 mm (t) and those of the n-type elements were 3.0 mm × 3.0 mm × 7.6 mm (t). The open circuit voltage was 1.9 V and the maximum output power was 1.4 W at a heat source temperature of 873 K and a cooling water temperature of 283 K in air.

The continues development of thermoelectric generators causes a permanent improvement of their characteristics. New types of thermoelectric generators can work at temperatures up to 1000 K. With this, special measurement equipment is needed to control the electrical parameters of the new developed specimens. The devices must be tested over the whole range of operating temperatures. For each temperature value a series of electrical measurements has to be performed. To establish the maximal output power of the thermoelectric generators, a load resistor with variable resistance has to be connected to the output of thermoelectric generator. The measurement system should measure the electrical current through the load resistor and the voltage over this resistor to determine the device parameters. A large amount of measurement data have to be collected and processed to evaluate the electrical characteristics of the specimen and to present them in graphical form, suitable for the comparison with others specimens.

The efficiency of a tantalum nitride interlayer as a diffusion barrier for CeFe4Sb12 thermoelectric material against electrode copper material has been investigated. The thermal stability of CeFe4Sb12/TaN/Cu stackings has been investigated after annealing at 600°C from a microstructural study. CeFe4Sb12 and Cu appear to chemically react through the formation of CeCu2 and Cu2Sb phases whereas no reaction is observed for CeFe4Sb12 with TaN. This study showed that the TaN interlayer cannot inhibit the diffusion of Sb from the skutterudite substrate to the copper electrode but prevents the diffusion of Ce and consequently the formation of the CeCu2 phase.

Roughly a decade ago an outstanding thermoelectric figure of merit ZT of 2.4 was reported for nanostructured Bi2Te3/Sb2Te3-based thin film superlattice (SL) structures. The published results strongly fueled and renewed the interest in the development of efficient novel nanostructured thermoelectric materials. This review article shall give an overview over the most recent theoretical and experimental advances on Bi2Te3/Sb2Te3 SLs and related superlattice systems. The presented theoretical models are subdivided into electronic and phononic aspects. The experimental results are summarized with regard to the method used. A more detailed elaboration on structural and transport properties is given in the subsequent sections.

Thermoelectric phenomena strongly influence the behavior of chalcogenide materials in nanoelectronic devices including phase-change memory cells. This paper presents the annealing temperature and phase dependent thermoelectric properties of Ge2Sb2Te5 films including the thermoelectric power factor and the figure of merit. The Ge2Sb2Te5 films annealed at different temperatures contain varying fractions of the amorphous and crystalline phases which strongly influence the thermoelectric properties. The thermoelectric power factor increases fom 3.2 μW/mK2 to 65 μW/mK2as the crystal phase changes from face-centered cubic to hexagonal close-packed. The data are consistent with modeling based on effective medium theory and suggest that careful consideration of phase purity is needed to improve the figures of merit for phase change memories and potentially for thermoelectric energy conversion applications.

Mg–Si thin films were fabricated on glass, Si(100), Si(111), and polycrystalline Al2O3 substrates by radio-frequency (RF) magnetron sputtering deposition using an elemental composite target composed of Si chips on a Mg disk. The effect of deposition conditions such as the composition ratio of Mg/Si in the target area, substrate temperature, and the type of substrate on the thin film deposition was investigated. By controlling the deposition conditions, pure-phase Mg2Si polycrystalline films were successfully fabricated at room temperature. The crystalline orientation of the films was strongly influenced by the Mg/Si elemental composition ratio in the targets as well as by the surface roughness and porosity of the substrate. The electron concentration and mobility of nondoped Mg2Si films were 2.2 × 1016 cm-3 and 2.0 cm2/Vs, respectively. The electron concentration of Mg2Si films was drastically increased by impurity doping with Al and Bi.

The poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) based ferroelectric and relaxor materials have been proved to be good electrocaloric (EC) materials. To further enhance the EC effect in ferroelectric relaxor terpolymer poly(vinylidene fluoride–trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)), composites such as polymer-polymer blends and nanocomposites filled with inorganic nanoparticles are fabricated and investigated. It is found that the addition of small amount of filler (such as P(VDF-TrFE) or nano-ZrO2) can increase terpolymer’s crystallinity and enhance its relaxor behavior through interface couplings. The increased crystallinity and enhanced relaxor behavior together result in enhanced electrocaloric effect. The results demonstrate the promise of composite approaches in tailoring and enhancing ECE in the relaxor terpolymers.