High temperature thermoelectric properties of Zn-doped Eu_5In_2Sb_6

Abstract

The complex bonding environment of many ternary Zintl phases, which often results in low thermal conductivity, makes them strong contenders as thermoelectric materials. Here, we extend the investigation of A_5In_2Sb_6 Zintl compounds with the Ca_5Ga_2As_6 crystal structure to the only known rare-earth analogue: Eu_5In_2Sb_6. Zn-doped samples with compositions of Eu_5In_(2−x)ZnxSb_6 (x = 0, 0.025, 0.05, 0.1, 0.2) were synthesized via ball milling followed by hot pressing. Eu_5In_2Sb_6 showed significant improvements in air stability relative to its alkaline earth metal analogues. Eu5In2Sb6 exhibits semiconducting behavior with possible two band behavior suggested by increasing band mass as a function of Zn content, and two distinct transitions observed in optical absorption measurements (at 0.15 and 0.27 eV). The p-type Hall mobility of Eu_5In_2Sb_6 was found to be much larger than that of the alkaline earth containing A_5In_2Sb_6 phases (A = Sr, Ca) consistent with the reduced hole effective mass (1.1 me). Zn doping was successful in optimizing the carrier concentration, leading to a zT of up to 0.4 at ∼660 K, which is comparable to that of Zn-doped Sr_5In_2Sb_6.

Additional Information

© 2015 Royal Society of Chemistry. Received 4 June 2015, Accepted 31 July 2015; first published online 31 July 2015. This research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration and was supported by the NASA Science Missions Directorate's Radioisotope Power Systems Technology Advancement Program. U.A. acknowledges the financial assistance of The Scientific and Technological Research Council of Turkey. We would like to acknowledge the Molecular Materials Research Center (MMRC) at Caltech for allowing use of their instruments for the optical measurements obtained in this work.

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