Antimony Vibrations in Skutterudites Probed by ¹²¹Sb Nuclear Inelastic Scattering

The specific lattice dynamic properties of antimony in the unfilled CoSb3 and filled EuFe4Sb12 skutterudites have been determined by nuclear inelastic scattering at the 121Sb nuclear resonance energy of 37.1298(2) keV with a 4.5 meV high-resolution backscattering sapphire monochromator. The Sb partial vibrational density of states (DOS) shows a maximum centered at 17 and 16 meV in CoSb3 and EuFe4Sb12, respectively. The difference between the Sb DOSs of CoSb3 and EuFe4Sb12 reveals that upon filling there is a transfer of 10% of the vibrational states toward lower energy. Further, a likely indication of the coupling between the guest and the host lattice in rattler systems is observed, a coupling that is required to reduce the lattice thermal conductivity