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

Abstract

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) ų, 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.