Vibrational dynamics of the filled skutterudite Yb1-xFe4Sb12: Debye-Waller factor, generalized density of states, and elastic structure factor

We discuss the temperature (T) dependence of the generalized density of states G(omega, T) and of the phonon intensities of the filled skutterudite compound YbFe4Sb12 investigated by inelastic neutron scattering in an extensive range of energy-momentum phase space. The inelastic response has been measured at T = 1.7, 50, 100, 200, and 290 K at a thermal time-of-flight spectrometer with an incident wavelength of 1.3 angstrom. The experimentally determined signal is compared with T-dependent ab initio powder averaged lattice dynamics calculations. An additional set of T-dependent spectra is calculated with thermal displacement parameters extracted from neutron diffraction data within the incoherent approximation. G(omega, T) shows a nonuniform intensity variation with T due to the specific thermal displacement parameters of Yb, Fe, and Sb. We demonstrate that this temperature variation can be well reproduced by the two simulation approaches. In particular, the ab initio powder averaged lattice dynamics calculation is capable of reproducing the momentum and energy characteristics of the phonon form factors of YbFe4Sb12.