High temperature thermoelectric properties of Zn-doped Eu5In2Sb6

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 A₅In₂Sb₆ Zintl compounds with the Ca₅Ga₂As₆ crystal structure to the only known rare-earth analogue: Eu₅In₂Sb₆. Zn-doped samples with compositions of Eu₅In_2−xZn_xSb₆ (x = 0, 0.025, 0.05, 0.1, 0.2) were synthesized via ball milling followed by hot pressing. Eu₅In₂Sb₆ 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 Eu₅In₂Sb₆ was found to be much larger than that of the alkaline earth containing A₅In₂Sb₆ phases (A = Sr, Ca) consistent with the reduced hole effective mass (1.1 m_e). 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 Sr₅In₂Sb₆.