Enhanced thermoelectric performance of skutterudite Co_1−yNi_ySn_1.5Te_1.5−x with switchable conduction behavior

A fine control of carriers in solids is the most essential thing while exploring any functionality. For a ternary skutterudite like CoSn_1·5Te_1.5−x, which has been recently recognized as a potential material for thermoelectric conversion, the dominant carrier could be either electrons or holes via chemically tuning the quaternary Sn₂Te₂ rings in the structure. Both theoretical calculation and different spectroscopic probes, such as X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) were employed to unveil the conduction type switching details. On the other hand, a Ni-for-Co substitution was applied to enhance electronic transport, and thereby the thermoelectric power factor. Thanks to the substantial cut-off of lattice thermal conductivity by the characteristic Sn₂Te₂ rings in the skutterudite structure, ultimately a 70-fold increase in the dimensionless figure-of-merit (zT) is achieved at 723 K with the nominal composition Co_0·95Ni_0·05Sn_1·5Te_1.5.