Vibrational dynamics of filled skutterudites M_1−xFe₄Sb₁₂ (M=Ca, Sr, Ba, and Yb)

First-principles density-functional theory and lattice-dynamics calculations were performed to study the vibrational dynamics and related observables of the ternary compounds Ca_1−xFe₄Sb₁₂, Sr_1−xFe₄Sb₁₂, Ba_1−xFe₄Sb₁₂. and Yb_1−xFe₄Sb₁₂. The calculation results are supported by experimental data, which were obtained from neutron inelastic scattering, neutron-diffraction, and heat-capacity measurements. Within the calculation approach based on the theory of harmonic solids all observables are linked to the phonon density of states Z(ω). The good agreement with experimental data shows that the vibrational dynamics of the ternary skutterudite structures can be described by a set of normal modes. Features in the experimentally obtained density of states G(ω) reflecting the variation in properties (mass, ionic radius) of the cations Ca, Sr, Ba, and Yb are reproduced by the calculations. The quality of the inelastic neutron experiments enables the detection of at least two mode peaks at 4.9 and 5.7 meV with a pronounced spectral weight of ytterbium.