Antimony vibrations in skutterudites probed by Sb-121 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 Sb-121 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