Filled skutterudites have shown promise as semiconducting materials with superior thermoelectric properties at temperatures up to at least 650 °C. This finding is a breakthrough in a continuing investigation of the potential utility of skutterudites as thermoelectric materials. Previous results of this investigation were reported in several articles in NASA Tech Briefs; namely, "Skutterudite Compounds for Power Semiconductor Devices" (NPO-19378), NASA Tech Briefs, Vol. 20, No. 3 (March 1996), page 60; "Two Potentially Useful Ternary Skutterudite Compounds" (NPO-19409), NASA Tech Briefs, Vol. 20, No. 11 (November 1996), page 66; and "Preparation and Some Properties of n-Type IrxCo1 — xSb3" (NPO-19852), NASA Tech Briefs, Vol. 20, No. 11 (November 1996), page 94.

ZT vs. Tempaerature was calculated from measurements on filled skutterudites and on three state-of-the-art thermoelectric materials; namely, PbTe, a Si/Ge alloy, and a Te/Ag/Ge/Sb ('TAGS') alloy.
Filled skutterudites are derived from the skutterudite crystal structure and can be represented by the formula LnT4Pn12; where "Ln" denotes one of the rare-earth elements La, Ce, Pr, Nd, Sm, Eu, Gd, Th, or U; "T" denotes Fe, Ru, Os, Co, Rh, or Ir; and "Pn" denotes one of the pnicogen elements P, As, or Sb. A skutterudite is said to be filled when empty octants in the skutterudite structure of T4Pn12 are filled with rare-earth atoms.

Some of the filled skutterudites of various compositions prepared by a combination of melting and powder-metallurgy techniques have shown exceptional thermoelectric properties in the temperature range of 350 to 700 °C. Both p-type (electron-acceptor) and n-type (electron-donor) conductivities have been obtained; this is fortunate in that to be functional, a thermoelectric device must contain layers of both types.

The thermoelectric figure of merit, ZT, is given by ZT = S2T/rl, where S is the Seebeck coefficient, T is the absolute temperature, r is the electrical resistivity, and l is the thermal conductivity. The figure shows ZT values obtained from measurements on several filled skutterudites and on other, state-of-the-art thermoelectric materials. One specimen exhibited ZT of almost 1.8 at a temperature of 650 °C; this is the highest ZT ever obtained since the beginning of thermoelectric technology in the 1950s. By manipulating the nominal compositions and doping concentrations of filled skutterudites, it may be possible to obtain similarly high ZT at lower and/or higher temperatures. These high-performance thermoelectric materials could be used to make thermoelectric power generators, coolers, and detectors that would operate with efficiencies greater than those of the corresponding devices now in use and could thus be useful in a greater variety of applications.

This work was done by Jean-Pierre Fleurial, Alexander Borshchevsky, Thierry Caillat, Donald Morelli, and Gregory Meisner of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp  under the Materials category.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to

Technology Reporting Office
JPL
Mail Stop 249-103
4800 Oak Grove Drive
Pasadena, CA 91109
(818) 354-2240

Refer to NPO-19909, volume and number of this NASA Tech Briefs issue, and the page number.

Topics:
Alloys Conductivity Electronic equipment Materials Materials properties Metals Semiconductor devices
This Brief includes a Technical Support Package (TSP).
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Filled Skutterudites as Thermoelectric Materials

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NASA Tech Briefs Magazine

This article first appeared in the June, 2001 issue of NASA Tech Briefs Magazine (Vol. 25 No. 6).

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Overview

The document is a technical support package prepared by the Jet Propulsion Laboratory (JPL) under a contract with NASA, focusing on filled skutterudites as thermoelectric materials. It is part of NASA Tech Brief Vol. 25, No. 6, dated June 1, 2001. The authors of the report include notable researchers Alexander Borshchevsky, Donald T. Morelli, Gregory P. Meisner, Jean-Pierre Fleurial, and Thierry Caillat.

Filled skutterudites are a class of materials that have garnered significant interest for their thermoelectric properties, particularly between 1957 and 1963. These materials are characterized by their ability to convert temperature differences into electrical voltage, making them valuable for applications in power generation and refrigeration. The document discusses the composition of these materials, which typically includes a specific arrangement of atoms within their crystal structure, noted to have 32 atoms per cell.

The report emphasizes the potential of filled skutterudites to operate effectively at high temperatures, reaching up to 650 °C. This capability is crucial for applications in aerospace and other high-temperature environments where traditional thermoelectric materials may fail. The document outlines the research conducted at JPL, highlighting the advancements made in understanding the properties and applications of these materials.

Additionally, the document includes a disclaimer stating that references to specific commercial products or manufacturers do not imply endorsement by the U.S. Government or JPL. It also notes that the work was carried out under NASA's sponsorship, emphasizing the collaborative nature of the research.

Overall, the document serves as a comprehensive overview of the research on filled skutterudites, detailing their significance in the field of thermoelectric materials and their potential applications in various technological domains. It reflects the ongoing efforts to explore and develop advanced materials that can enhance energy efficiency and performance in demanding environments.