Observation of Square-Planar Distortion in Lanthanide-Doped Skutterudite Crystals

Abstract

Skutterudite crystals are of interest for their thermoelectric properties and in particular for the flexibility the structure offers for tuning such properties. One strategy to enhance the thermoelectric capabilities of these structures is to dope the “cage” site to disrupt phonon modes. Observation of such changes in these structures on the atomic scale is challenging, however, and understanding atomic-scale changes is crucial to understanding its macroscopic properties. Here, a series of polycrystalline Co2Ni2Sb8Sn4 skutterudites doped with Ce, Dy, and Yb were synthesized. Using scanning transmission electron microscopy, we observe small tilts in the square-planar Sb–Sn rings. Using density functional theory to calculate a relaxed structure, we attribute these distortions to under-bonding of the rings with the lanthanide dopants.