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 A(5)In(2)Sb(6) Zintl compounds with the Ca5Ga2As6 crystal structure to the only known rare-earth analogue: Eu5In2Sb6. Zn-doped samples with compositions of Eu5In2-xZnxSb6 (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 semi-conducting 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 A(5)In(2)Sb(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 similar to 660 K, which is comparable to that of Zn-doped Sr5In2Sb6.