Many of the recent advances in enhancing the thermoelectric figure of merit are linked to nanoscale phenomena found both in bulk samples containing nanoscale constituents and in nanoscale samples themselves. Prior theoretical and experimental proof-of-principle studies on quantum-well superlattice and quantum-wire samples have now evolved into studies on bulk samples containing nanostructured constituents prepared by chemical or physical approaches. In this Review, nanostructural composites are shown to exhibit nanostructures and properties that show promise for thermoelectric applications, thus bringing together low-dimensional and bulk materials for thermoelectric applications. Particular emphasis is given in this Review to the ability to achieve 1) a simultaneous increase in the power factor and a decrease in the thermal conductivity in the same nanocomposite sample and for transport in the same direction and 2) lower values of the thermal conductivity in these nanocomposites as compared to alloy samples of the same chemical composition. The outlook for future research directions for nanocomposite thermoelectric materials is also discussed.

https://www.bc.edu/content/dam/files/schools/cas_sites/physics/pdf/Ren/AdvMater_19_1043_2007.pdf

New Directions for Low-Dimensional Thermoelectric Materials**

The conversion of heat to electricity by thermoelectric devices may play a key role in the future for energy production and utilization. However, in order to meet that role, more efficient thermoelectric materials are needed that are suitable for high-temperature applications. We show that the material system AgPb m SbTe 2+ m may be suitable for this purpose. With m = 10 and 18 and doped appropriately, n -type semiconductors can be produced that exhibit a high thermoelectric figure of merit material ZT max of ∼2.2 at 800 kelvin. In the temperature range 600 to 900 kelvin, the AgPb m SbTe 2+ m material is expected to outperform all reported bulk thermoelectrics, thereby earmarking it as a material system for potential use in efficient thermoelectric power generation from heat sources.

http://science.sciencemag.org/content/sci/303/5659/818.full.pdf

Cubic AgPbmSbTe2+m: Bulk Thermoelectric Materials with High Figure of Merit

Herein we cover the key concepts in the field of thermoelectric materials research, present the current understanding, and show the latest developments. Current research is aimed at increasing the thermoelectric figure of merit (ZT) by maximizing the power factor and/or minimizing the thermal conductivity. Attempts at maximizing the power factor include the development of new materials, optimization of existing materials by doping, and the exploration of nanoscale materials. The minimization of the thermal conductivity can come through solid-solution alloying, use of materials with intrinsically low thermal conductivity, and nanostructuring. Herein we describe the most promising bulk materials with emphasis on results from the last decade. Single-phase bulk materials are discussed in terms of chemistry, crystal structure, physical properties, and optimization of thermoelectric performance. The new opportunities for enhanced performance bulk nanostructured composite materials are examined and a look into the not so distant future is attempted.

New and Old Concepts in Thermoelectric Materials

An introduction to heat transfer

A class of thermoelectric materials has been synthesized with a thermoelectric figure of merit ZT (where T is temperature and Z is a function of thermopower, electrical resistivity, and thermal conductivity) near 1 at 800 kelvin. Although these materials have not been optimized, this value is comparable to the best ZT values obtained for any previously studied thermoelectric material. Calculations indicate that the optimized material should have ZT values of 1.4. These ternary semiconductors have the general formula RM4X12 (where R is lanthanum, cerium, praseodymium, neodymium, or europium; M is iron, ruthenium, or osmium; and X is phosphorus, arsenic, or antimony) and represent a new approach to creating improved thermoelectric materials. Several alloys in the composition range CeFe4-xCoxSb12 or LaFe4-xCoxSb12 (0 < x < 4) have large values of ZT.

https://science.sciencemag.org/content/sci/272/5266/1325.full.pdf

Filled Skutterudite Antimonides: A New Class of Thermoelectric Materials

We have fabricated and studied the structural, magnetic, and transport properties of filled skutterudites of the form Ce{sub y}Fe{sub 4{minus}x}Co{sub x}Sb{sub 12} with 0{lt} y{lt}1 and x=3.25 and 4. For samples containing 100{percent} Co, Ce can be inserted into approximately 10{percent} of the voids in the skutterudite structure. It is shown that the rare earth is trivalent and dopes the host CoSb{sub 3} n-type. With substitution of Fe for Co the void occupancy by Ce increases. The thermal conductivity is strongly depressed even at small (5{percent}) rare-earth filling fractions, and is further degraded by substitution of Fe for Co. Although the electron mobility in n-type samples is smaller than the hole mobility in p-type samples, due to their large electron masses the Seebeck coefficient in n-type material maintains large values at high electron concentrations. {copyright} {ital 1997} {ital The American Physical Society}

Cerium filling and doping of cobalt triantimonide

Single crystals of the skutterudite ${\mathrm{CoSb}}_{3}$ exhibit large hole mobilities (up to 3000 ${\mathrm{cm}}^{2}$ ${\mathrm{V}}^{\mathrm{\ensuremath{-}}1}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ at room temperature), intrinsic lattice thermal conductivity down to 10 K, and pronounced phonon drag effects in the thermoelectric power. The dependence of the mobility and diffusion thermopower on hole density is consistent with recent band-structure calculations, which indicate that ${\mathrm{CoSb}}_{3}$ possesses a highly nonparabolic valence-band structure.

Low-temperature transport properties of p-type cosb3

Thermal conductivity, thermoelectric power, electrical resistivity, Hall coefficient, and magnetic susceptibility of the filled skutterudites ${\mathrm{CeFe}}_{4\mathrm{\ensuremath{-}}\mathrm{x}}$ ${\mathrm{Co}}_{\mathrm{x}}$ ${\mathrm{Sb}}_{12}$ , with x=0, 0.5, 1.0, 1.5, and 2.0, have been studied from 2 to 300 K. We find that the substitution of Co at Fe sites has a dramatic effect on all transport properties. While the resistivity of ${\mathrm{CeFe}}_{4}$ ${\mathrm{Sb}}_{12}$ has a metallic character, substitution of Co leads to a progressively stronger activated behavior and a decrease in hole concentration. The thermopower increases with increasing Co, while the thermal conductivity is depressed, notably at low temperatures. Susceptibility data suggest the presence of large effective moments. At high temperatures Ce is nearly trivalent, but valence fluctuations prevail at low temperatures. Strong hybridization of the Ce 4f states with the Fe 3d and pnicogen p states appears to be important in understanding the physical properties of these compounds.

Low-temperature transport properties of the filled skutterudites CeFe 4 − x Co x Sb 12 s

A non-optical isolator having a driver circuit for providing an input signal to one or more first passive components which are coupled across a galvanic isolation barrier to one or more corresponding second passive components, and an output circuit that converts the signal from the second passive components to an output signal corresponding to the input signal. The entire structure may be formed monolithically as an integrated circuit on one or two die substrates, for low cost, small size, and low power consumption. The passive components may be coils (140, 142) or capacitor plates (130, 132, 134, 136), for example. When the first and second passive components are capacitor plates, a Faraday shield (51) may be provided between them, with the first and second passive components being referenced to separate grounds and the Faraday shield (51) referenced to the same ground as the second passive components.

Non-optical signal isolator

A logic signal isolator comprising a transformer having a primary winding and a secondary winding; a transmitter circuit which drives said primary winding in response to a received logic signal, such that in response to a first type of edge in the logic signal, a signal of a first predetermined type is supplied to the primary winding and in response to a second type of edge in the logic signal, a signal of a second predetermined type is supplied to said primary winding, the primary winding and the transmitter being referenced to a first ground; and the secondary winding being referenced to a second ground which is galvanically isolated from the first ground and said secondary winding supplying to a receiver circuit signals received in correspondence to the signals provided to the primary winding, the receiver reconstructing the received logic signal from the received signals.

Baoxing Chen

Papers

Cerium filling and doping of cobalt triantimonide

Low-temperature transport properties of p-type cosb3

Low-temperature transport properties of the filled skutterudites CeFe 4 − x Co x Sb 12 s

Non-optical signal isolator

Signal isolators using micro-transformers