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Published June 25, 2019 | Supplemental Material
Journal Article Open

Synthesis and Characterization of Vacancy-Doped Neodymium Telluride for Thermoelectric Applications

Abstract

Thermoelectric materials exhibit a voltage under an applied thermal gradient and are the heart of radioisotope thermoelectric generators (RTGs), which are the main power system for space missions such as Voyager I, Voyager II, and the Mars Curiosity rover. However, materials currently in use enable only modest thermal-to-electrical conversion efficiencies near 6.5% at the system level, warranting the development of material systems with improved thermoelectric performance. Previous work has demonstrated large thermoelectric figures of merit for lanthanum telluride (La_(3–x)Te_4), a high-temperature n-type material, achieving a peak zT value of 1.1 at 1275 K at an optimum cation vacancy concentration. Here, we present an investigation of the thermoelectric properties of neodymium telluride (Nd_(3–x)Te_4), another rare-earth telluride with a structure similar to La_(3–x)Te_4. Density functional theory (DFT) calculations predicted a significant increase in the Seebeck coefficient over La_(3–x)Te_4 at equivalent vacancy concentrations because of an increased density of states (DOS) near the Fermi level from the 4f electrons of Nd. The high-temperature electrical resistivity, Seebeck coefficient, and thermal conductivity were measured for Nd_(3–x)Te_4 at various carrier concentrations. These measurements were compared to La_(3–x)Te_4 in order to elucidate the impact of the four 4f electrons of Nd on the transport properties of Nd_(3–x)Te_4. A zT of 1.2 was achieved at 1273 K for Nd_(2.78)Te_4, which is a 10% improvement over that of La_(2.74)Te_4.

Additional Information

© 2019 American Chemical Society. Received: March 8, 2019; Revised: May 15, 2019. Publication Date: June 11, 2019. The authors would like to extend special thanks to Greg Gerig and George Nakatsukasa for their aid with high-temperature measurements. Additionally, we would like to thank Chi Ma at the California Institute of Technology for his assistance performing EPMA. This work was performed at the California Institute of Technology/Jet Propulsion Laboratory under contract with the National Aeronautics and Space Administration and was supported by the NASA Science Missions Directorate's Radioisotope Power Systems Program. The project is based upon work supported by the National Science Foundation under grant 1102531 awarded to H. Gillman, and was also supported by the National Institute of General Medical Sciences of the National Institutes of Health under award number R25GM055052 awarded to T. Hasson. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. The work was also supported by Caltech Summer Undergraduate Research Fellowship. Author Contributions: S.J.G. and D.C. contributed equally to this work. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. The authors declare no competing financial interest.

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