Vibrational dynamics of the filled skutterudites M1-xFe4Sb12 (M = Ca, Sr, Ba, and Yb): Temperature response, dispersion relation, and material properties

The vibrational dynamics of the ternary Ca1-xFe4Sb12, Ba1-xFe4Sb12, Sr1-xFe4Sb12, and Yb1-xFe4Sb12 compounds is studied for its temperature dependence, dispersion relations, and material properties by experiments and ab initio powder-averaged lattice-dynamics (PALD) calculations. The experimental techniques used are high-resolution inelastic neutron scattering (INS) and inelastic x-ray scattering (IXS). Vibrational properties of polycrystalline material have been mapped out in an extensive energy-momentum phase space facilitating the study of powder-averaged phonon-dispersion relations within the first and second Brillouin zones. Qualitatively, the experimental dynamic structure factor S(Q,omega) matches, to a high degree, PALD calculations allowing different schemes of collective vibrational eigenmodes to be evaluated. From the PALD calculations, quantitative values of velocity of sound, Debye temperatures, and elastic, bulk, and Young's moduli are computed. The variation of the generalized density of states G(omega) with temperature is studied experimentally in the range from 2 to 600 K. No particular anomalies in the collective dynamics are observed apart from a global softening of G(omega) upon heating.