Enhanced Thermoelectric Performance of Yb-Single-Filled Skutterudite by Ultralow Thermal Conductivity

The filling fraction limitation (FFL) in n-type CoSb3 skutterudites is far below that of p-type (Fe,Co)Sb3-based skutterudites, and it is critical to increase FFL for accomplishing high thermoelectric figure of merit (ZTmax). Here, a series of YbxCo4–yFeySb12 alloys with x = 0.25–0.5 and y = 0.1–0.5 were synthesized, which demonstrate a clear increase of the FFL of Yb from ∼0.3 in CoSb3 to 0.5. Ultralow thermal conductivities of 2.0–2.5 W/m·K at 300 K and 1.75 W/m·K at ∼600 K have been achieved, which are the lowest values reported among skutterudite materials and comparable with p-type skutterudites. These ultralow thermal conductivities result from the combination of secondary phase scattering and phonon scattering from dynamic electron exchange between Fe2+ and Co3+. High ZTmax values of 1.28 at 740 K and 1.34 at 780 K are obtained, which are among the best values reported in the temperature range of 740–800 K. The temperature at which maximum ZTmax appears is shifted below 850 K. These results are highly exciting toward the development of multistage segmented and cascade thermoelectric power generators for in-air operations.