Thermoelectric materials, which can generate electricity from waste heat or be used as solid-state Peltier coolers, could play an important role in a global sustainable energy solution. Such a development is contingent on identifying materials with higher thermoelectric efficiency than available at present, which is a challenge owing to the conflicting combination of material traits that are required. Nevertheless, because of modern synthesis and characterization techniques, particularly for nanoscale materials, a new era of complex thermoelectric materials is approaching. We review recent advances in the field, highlighting the strategies used to improve the thermopower and reduce the thermal conductivity.

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Complex thermoelectric materials.

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

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

There has been a renaissance of interest in exploring highly efficient thermoelectric materials as a possible route to address the worldwide energy generation, utilization, and management. This review describes the recent advances in designing high-performance bulk thermoelectric materials. We begin with the fundamental stratagem of achieving the greatest thermoelectric figure of merit ZT of a given material by carrier concentration engineering, including Fermi level regulation and optimum carrier density stabilization. We proceed to discuss ways of maximizing ZT at a constant doping level, such as increase of band degeneracy (crystal structure symmetry, band convergence), enhancement of band effective mass (resonant levels, band flattening), improvement of carrier mobility (modulation doping, texturing), and decrease of lattice thermal conductivity (synergistic alloying, second-phase nanostructuring, mesostructuring, and all-length-scale hierarchical architectures). We then highlight the decoupling of th...

Rationally Designing High-Performance Bulk Thermoelectric Materials

High-efficiency thermoelectric (TE) materials are important for power-generation devices that are designed to convert waste heat into electrical energy.They can also be used in solid-state refrigeration devices.The conversion of waste heat into electrical energy may play an important role in our current challenge to develop alternative energy technologies to reduce our dependence on fossil fuels and reduce greenhouse gas emissions. An overview of various TE phenomena and materials is provided in this issue of MRS Bulletin. Several of the current applications and key parameters are defined and discussed.Novel applications of TE materials include biothermal batteries to power heart pacemakers, enhanced performance of optoelectronics coupled with solid-state TE cooling, and power generation for deep-space probes via radioisotope TE generators.A number of different systems of potential TE materials are currently under investigation by various research groups around the world, and many of these materials are reviewed in the articles in this issue.These range from thin-film superlattice materials to large single-crystal or polycrystalline bulk materials, and from semiconductors and semimetals to ceramic oxides.The phonon-glass/electron-crystal approach to new TE materials is presented, along with the role of solid-state crystal chemistry.Research criteria for developing new materials are highlighted.

/pdf/thermoelectric-materials-phenomena-and-applications-a-bird-s-2e5bqpy32n.pdf

Thermoelectric materials, phenomena, and applications : A bird's eye view

The field of thermoelectric energy conversion is reviewed from both a theoretical and an experimental standpoint. The basic theory is introduced and the thermodynamic and solid state views are compared. An overview of the development of thermoelectric materials is presented with particular emphasis being placed on the most recent developments in high-temperature semiconductors. A number of possible device applications are discussed and the successful use and suitability of these devices for space power is manifest.

https://iopscience.iop.org/article/10.1088/0034-4885/51/4/001/pdf

C. Wood

Papers

Materials for thermoelectric energy conversion