Ultralow Thermal Conductivity and High Thermopower in a New Family of Zintl Antimonides Ca₁₀MSb₉ (M = Ga, In, Mn, Zn) with Complex Structures and Heavy Disorder

A new family of Zintl antimonides with the approximate composition Ca10MSb9 (M = Ga, In, Mn, Zn) has been obtained via two synthetic approaches: (1) using Sb as a flux and (2) using the conventional high-temperature method in welded Nb tubes. The new compounds crystallize in a disordered variant of the tetragonal Ca10LiMgSb9 structure type. The observed occupational and positional disorder serves as a means to retain a charge-balanced composition, which ultimately results in semiconducting behavior, predicted from first-principles and measured experimentally. High-temperature transport measurements reveal ultralow thermal conductivity (0.5–0.7 W·m–1·K–1), due to the extensive disorder, and high values of the Seebeck coefficient (100–200 μV·K–1 at T = 800 K). The highest thermoelectric figure of merit, zT = 0.2, exhibited by the In representative without any optimization, suggests that good thermoelectric performance can be achieved in this family of compounds.