Praseodymium Telluride: A High-Temperature, High-ZT Thermoelectric Material

• Published in: Joule Vol. 2; no. 4; pp. 698 - 709
• Main Authors: Cheikh, Dean, Hogan, Brea E., Vo, Trinh, Von Allmen, Paul, Lee, Kathleen, Smiadak, David M., Zevalkink, Alexandra, Dunn, Bruce S., Fleurial, Jean-Pierre, Bux, Sabah K.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 18.04.2018
• Subjects: electronic transport; lanthanum telluride; mechanochemical synthesis; praseodymium telluride; rare-earth chalcogenide; rare-earth telluride; thermal transport; thermoelectric; thermoelectric; praseodymium telluride; thermal transport; rare-earth chalcogenide; electronic transport; mechanochemical synthesis; rare-earth telluride; lanthanum telluride
• ISSN: 2542-4351; 2542-4351
• DOI: 10.1016/j.joule.2018.01.013

Refractory rare-earth tellurides with the Th3P4 structure type have attracted considerable interest as high-performance thermoelectric materials since the 1980s due to their high dimensionless figure of merit (ZT). Extensive work has been conducted on La3−xTe4 with peak ZT values greater than 1.1 at 1,273 K. The high ZT of La3-xTe4 is in part due to a large peak in the density of states near the Fermi level from the La 5d states. Here, we revisit Pr3−xTe4, for which our electronic structure calculations predict a favorable modification of the density of states by the introduction of praseodymium's 4f electrons. This was experimentally verified by preparing Pr3−xTe4 samples with varying Pr vacancy concentrations using a mechanochemical synthesis approach. The thermoelectric properties were measured and a ZT of 1.7 at 1,200 K was achieved with Pr2.74Te4. The 50% improvement in peak ZT compared with La3−xTe4 resulted from an increased effective mass, improved Seebeck coefficient, and lower thermal conductivity. [Display omitted] •Praseodymium has been known to have interesting optical and electronic properties•Investigated the effects of 4f electrons in Pr as a method of improving ZT•Pr2.74Te4 possesses a peak ZT = 1.7 at 1,200 K, the highest ZT reported above 1,000 K Thermoelectric generators have been an enabling technology for reliably powering many long-lived space science and exploration missions by the National Aeronautics and Space Administration such as the Voyager missions and the recent Mars rover, Curiosity. A significant increase in conversion efficiency by materials such as Pr3−xTe4 would translate into a reduction in the amount of expensive heat-source fuel and could allow for an increase in the available power as well as more capable payloads for a given mission. Beyond space applications, higher efficiencies would benefit the recent surge of interest in implementing thermoelectrics for terrestrial applications such as waste heat recovery from automobiles and industrial processes. Praseodymium is known to have interesting optical and electronic properties but has been underutilized in the thermoelectric community. We synthesized a series of Pr3−xTe4 compounds and verified their phase purity and composition via Rietveld refinement of X-ray data, wavelength dispersive spectroscopy, and Hall carrier concentration with excellent agreement with the nominal stoichiometry. Measurement of transport properties indicate we were able to achieve a peak ZT = 1.7 at 1,200 K, the highest figure of merit reported above 1,000 K.