Yb14MgBi11: structure, thermoelectric properties and the effect of the structure on low lattice thermal conductivity.

Zintl phases Yb14MnSb11 and Yb14MgSb11, 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, Yb14MgBi11, was synthesized in order to investigate the structure and thermoelectric properties of the Bi analogs. Yb14MgBi11 crystallizes in the Ca14AlSb11 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 Yb14MgBi11 are measured together with Yb14MnBi11 and both compounds are metallic. Compared to Yb14MgSb11, Yb14MgBi11 has a higher carrier concentration with a similar mobility and effective mass. The lattice thermal conductivity of Yb14MgBi11 is extremely low, which is as low as 0.16-0.36 W(mK)-1. The zT values of Yb14MgBi11 and Yb14MnBi11 reach 0.2 at 875 K.