Lattice dynamics of CeSn3

Abstract

Inelastic neutron scattering techniques have been used to measure the phonon dispersion curves of Ce${\mathrm{Sn}}_3$ at room temperature and the frequencies of a selected number of phonons at 10 K. We find that in the [111] symmetry direction the measured frequencies in the vicinity of the first $R_{25}^{\prime }$ zone-boundary point are considerably lower than those of the isostructural compound La${\mathrm{Sn}}_3$. Examination of the relative motion of the nuclei of Ce${\mathrm{Sn}}_3$ in this mode of vibration shows that this pronounced anomaly may be attributed to mixed-valence effects on the phonon frequencies. We did not observe, on the other hand, any significant anomalies in the widths of the measured neutron groups, and we estimated that any lifetime effects due to the electron-phonon coupling in Ce${\mathrm{Sn}}_3$ are certainly smaller than approximately 0.15 THz. Also we find that the temperature dependence of the phonon frequencies is normal and can be accounted for by the effect of the thermal expansion of the lattice on the vibrational frequencies. The force constants obtained by fitting the experimental data to a three-nearest-neighbor Born-von Kármán model were used to evaluate the phonon density of states, the lattice specific heat, and the atomic temperature factors of Ce and Sn in this compound.