Vibrational Dynamics of Filled Skutterudites La$T_{4}X_{12}$ ($T$ = Fe, Ru, Os, $X$ = As, Sb)

We report on the vibrational properties of the lanthanum filled skutterudite compounds LaRu 4 Sb 12 , LaOs 4 Sb 12 , and LaOs 4 As 12 studied by inelastic neutron scattering. The experimental data are backed up by ab initio lattice dynamics calculations of the complete series of lanthanum filled skutterudites La$T_{4}X_{12}$ with $T$ = Fe, Ru, Os and $X$ = As, Sb. We present details of their structural properties, phonon dispersion relations, vibrational densities of states $Z(\omega)$ and specific heats $C_{V}(T)$ calculated from $Z(\omega)$ within the harmonic approximation. Powder averaged lattice dynamics (PALD) technique is applied to approximate the experimental signal presented as the generalized density of states $G(\omega)$ with high accuracy. Furthermore, the PALD approach is exploited to compute average transverse $v_{\text{t}}^{\text{PALD}}$ and longitudinal $v_{\text{l}}^{\text{PALD}}$ sound velocities, elastic constants $c_{11}^{\text{PALD}}$, $c_{44}^{\text{PALD}}$, bulk moduli $B^{\text{PALD}}$, and Debye temperatures $\Theta_{\text{D}}^{\text{PALD}}$. The PALD results are compared with data computed from ab initio lattice dynamics calculations. All calculated properties are in very good agreement with literature data.