Enhanced thermoelectric performance in zinc substituted p-type filled skutterudites CeFe4−xZnxSb12

In this study, Zn-substituted polycrystalline skutterudites CeFe4−xZnxSb12 (x=0, 0.05, 0.1, 0.2, 0.3) were successfully prepared by a traditional melting–annealing method. The solubility of Zn in Fe site is ∼1.2%, exceeding which trace amount of ZnSb phase can be detected in the XRD. This ZnSb impurity phase, with size of several hundred nanometers for the sample with x=0.2 but showing surprisingly small size of ∼10 nm for the sample with x=0.3, selectively distributes on the grain boundaries. In particular, the introduction of Zn in Fe site effectively improves the Seebeck coefficient in a manner of enhancement in hole effective mass, but it has negligible influence on both electrical and thermal conductivities though the hole concentration is increased. Consequently the corresponding improvement in power factor leads to an improved thermoelectric figure of merit (ZT) of 0.9 at 800 K for the sample with x=0.1, which is ∼15% higher than that of Zn-free sample. This study demonstrates a favorable effect of Zn iso-substitution and opens a new strategy to improve the thermoelectric properties of p-type Fe-based skutterudites beyond the sole phonon engineering.