High temperature thermoelectric properties of Zn-doped Eu₅In₂Sb₆

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.