First-principles study of filled and unfilled skutterudite antimonies

TL;DR

This study uses density functional perturbation theory to analyze the electronic and vibrational properties of skutterudite antimonides, revealing how filling affects phonon behavior and dielectric responses.

Contribution

It provides a detailed first-principles analysis of filled and unfilled skutterudite antimonides, highlighting the origin of low-energy phonon peaks and unusual dielectric features due to filling.

Findings

Weak coupling of Tl vibrations with host crystal modes

Giant Born effective charges observed in filled compound

Strong increase in dielectric tensor upon filling

Abstract

The electron localization tensor, Born effective charges, dielectric constants and phonon dispersion relations of the skutterudite CoSb$_3$ and the filled skutterudite TlFeCo$_3$Sb$_{12}$ have been studied using density functional perturbation theory. The origin of the low energy peak in the phonon density of states of TlFeCo$_3$Sb$_{12}$ observed recently by Neutron inelastic scattering [R. P. Hermann {\it et al.}, Phys. Rev. Lett. {\bf 90}, 135505 (2003)] is attributed to the vibrations of Tl that show only weak coupling with the normal modes of the host crystal. Moreover, the dielectric properties of these materials show unsual features such as giant Born effective charges and a strong increase of the optical and static dielectric tensor in the filled compound.