Antimony vibrations in skutterudites probed by Sb121 nuclear inelastic scattering

The specific lattice dynamic properties of antimony in the unfilled Co Sb3 and filled Eu Fe4 Sb12 skutterudites have been determined by nuclear inelastic scattering at the Sb121 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 Co Sb3 and Eu Fe4 Sb12, respectively. The difference between the Sb DOSs of Co Sb3 and Eu Fe4 Sb12 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.