Yb 14 MgBi 11 : structure, thermoelectric properties and the effect of the structure on low lattice thermal conductivity.

Zintl phases Yb14 MnSb11 and Yb14 MgSb11 , which share the same complex structure type, have been demonstrated as the best p-type thermoelectric materials for the high temperature region (800-1200 K). A new iso-structural compound, Yb14 MgBi11 , was synthesized in order to investigate the structure and thermoelectric properties of the Bi analogs. Yb14 MgBi11 crystallizes in the Ca14 AlSb11 structure-type with the space group I41 /acd [a = 16.974(2) Å, c = 22.399(4) Å, V = 6454(2) Å3 , R1 /wR2 = 0.0238/0.0475]. The structure follows the previous description of this structure type and the trend observed in previous analogs. Thermoelectric properties of Yb14 MgBi11 are measured together with Yb14 MnBi11 and both compounds are metallic. Compared to Yb14 MgSb11 , Yb14 MgBi11 has a higher carrier concentration with a similar mobility and effective mass. The lattice thermal conductivity of Yb14 MgBi11 is extremely low, which is as low as 0.16-0.36 W(mK)-1 . The zT values of Yb14 MgBi11 and Yb14 MnBi11 reach 0.2 at 875 K.