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

The filling fraction limitation (FFL) in n-type CoSb ₃ skutterudites is far below that of p-type (Fe,Co)Sb ₃ -based skutterudites, and it is critical to increase FFL for accomplishing high thermoelectric figure of merit (ZT _max ). Here, a series of Yb _x Co _4-y Fe _y Sb ₁₂ 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 CoSb ₃ 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 Fe ²⁺ and Co ³⁺ . High ZT _max 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 ZT _max 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.