Advanced Thermoelectric Materials Research Articles

Joining of Mo to CoSb 3 by spark plasma sintering by inserting a Ti interlayer

Abstract CoSb 3-based skutterudite compounds are promising candidates as advanced thermoelectric (TE) materials used in TE power generation. The electrode fabrication is one of the key techniques in constructing TE elements for the practical application. In the present study, sintering of CoSb 3 powder and joining of CoSb 3 to molybdenum electrode have been simultaneously performed by spark plasma sintering (SPS) technique. The insertion of Ti interlayer between Mo and CoSb 3 is effective to join CoSb 3 to Mo by forming an intermediate layer of TiSb at the Ti–CoSb 3 boundary and a composition–gradient alloy layer at the Ti–Mo boundary. Potential voltage measurement results indicated that CoSb 3/Ti/Mo joint interface has a low electrical resistance. The CoSb 3/Ti/Mo joints also have a moderately high shearing strength and high thermal duration stability.

Nano-dendrites in NaFe4P12 nano-wires synthesized by hydrothermal method

Abstract Skutterudite is one of the most promising thermoelectric (TE) semiconductor materials. Last year, NaFe4P12 skutterudite nano-wires have been synthesized by our group, and may potentially be used for preparing advanced TE materials with a quantum structure. Recently, we found that there are some nano-dendrites in the NaFe4P12 nano-wires, which can be used in some special electronic components to connect the nano-wires as nano-joints. In this paper, the morphology and growth mechanism of NaFe4P12 nano-dendrites are reported. The angles between two branches are 60° or 120°. Electron diffraction shows that the orientation plane of the dendrites is (1 1 1). The formation of the dendrites is caused by defects in the nano-wires.

Solar thermolectric generator based on skutterudites

A numerical simulation based on the optimal control theory was developed to assess the performances, dimensions and weight characteristics of skutterudite-based solar thermoelectric generators (STG) for satellite missions at distances close to the Sun. It is shown that the STG designs based on these advanced thermoelectric materials are potentially attractive for this type of application and could advantageously replace the standard power sources such as the solar (cells) panel or the radioisotope thermoelectric generators.

Progress in the development of segmented thermoelectric unicouples at the Jet Propulsion Laboratory

ABSTRACTA new version of a segmented thermoelectric unicouple incorporating advanced thermoelectric materials with superior thermoelectric figures of merit has been recently proposed and is currently under development at the Jet Propulsion Laboratory (JPL). This advanced segmented thermoelectric unicouple includes a combination of state-of-the-art thermoelectric materials based on Bi2Te3 and novel materials developed at JPL. The segmented unicouple currently being developed is expected to operate between 300 and about 975K with a projected thermal to electrical efficiency of up to 15%. The segmentation can be adjusted to accommodate various hot-side temperatures depending on the specific application envisioned. Techniques and materials have been developed to bond the different thermoelectric segments together for the nand p-legs and low contact resistance bonds have been achieved. In order to experimentally determine the thermal to electrical efficiency of the unicouple, metallic interconnects must be developed for the hot side of the thermocouple to connect the n- and p-legs electrically. The latest results in the development of these interconnects are described in this paper. Efforts are also focusing on the fabrication of a unicouple specifically designed for thermal and electrical testing.

Growth and some properties of Cr 11Ge 19

Cr 11Ge 19 belongs to a large family of materials known as the Nowotny chimney-ladder compounds, some of which were recently proposed as advanced thermoelectric materials, particularly because of their low thermal conductivity related to their relatively complex crystal structure. In order to assess the potential of the compound Cr 11Ge 19 for thermoelectric applications, we grew large single crystals of this peritectic compound by a vertical gradient freeze technique and measured the thermoelectric properties of the crystals. Cr 11Ge 19 forms peritectically at 1201 K and crystals were grown from Ge-rich solutions. The conditions and the results of the crystal growth experiments are presented. The crystals were characterized by X-ray diffractometry, Laue technique, and electron probe microanalysis. The results of the thermoelectric property measurements suggest that Cr 11Ge 19 has a metallic behavior and therefore presents little interest for thermoelectric applications.

Advanced Thermoelectric Materials and Systems for Automotive Applications in the Next Millennium

AbstractA combination of environmental, economic, and technological drivers has led to a reassessment of the potential for using thermoelectric devices in several automotive applications. In order for this technology to achieve its ultimate potential, new materials with enhanced thermoelectric properties are required. Experimental results on the fundamental physical properties of some new thermoelectric materials, including filled skutterudites and 1–1–1 intermetallic semiconductors, are presented.

Bridgman-solution crystal growth and characterization of the skutterudite compounds CoSb3 and RhSb3

Compounds with the skutterudite structure have recently been identified as advanced thermoelectric materials. We report on the crystal growth and characterization of the skutterudite compounds CoSb3 and RhSb3 which form peritectically at 873 and 900°C, respectively. Large single crystals were obtained by the vertical gradient freeze technique from solutions rich in antimony. The samples were characterized by high-temperature Hall-effect and electrical resistivity measurements. Bandgaps of 0.56 and 0.80 eV were estimated from these measurements for CoSb3 and RhSb3, respectively. N-type CoSb3 samples were obtained by doping with Te. Exceptionally high p-type Hall-mobility values have been measured and a room-temperature value of 3445 cm2 V−1 s−1 was obtained for CoSb3 at a carrier concentration of 4 × 1017 cm−3 and 8000 cm2 V−1 s−1 was obtained for RhSb3 at a carrier concentration of 3.5 × 1018 cm−3.

Low temperature properties of the filled skutterudite CeFe4Sb12

CeFe4Sb12 is a member of a class of advanced thermoelectric materials. In order to evaluate this material’s potential for such applications, we have measured a variety of its properties at low temperature, including thermal conductivity, thermoelectric power, electrical resistivity, Hall coefficient, and magnetic susceptibility.

Technology development issues in space nuclear power for planetary exploration

Planning for future planetary exploration missions indicates that there are continuing, long range requirements for nuclear power, and in particular radioisotope-based power sources. In meeting these requirements, there is a need for higher efficiency, lower mass systems. We describe here four technology areas currently under development that address these goals: modular RTG, modular RTG with advanced thermoelectric materials, dynamic isotope power system(DIPS), and the Alkali Metal Thermoelectric Converter(AMTEC). The modular RTG is the next generation improvement in RTG performance, where work is now focussed on development of the multicouple converter technology. If advances are also made in thermoelectric materials, the modular RTG may provide as much as 10 W/kg at 10% efficiency. The DIPS technology, at much higher efficiencies, would enable multikilowatt radioisotope power if reliable, long term, continuous operation under space conditions can be assured. Finally, while static AMTEC devices offer the potential for efficiencies comparable to dynamic systems, this technology is the least mature of those discussed, and will require the demonstration of several component technologies in long life tests.