Lattice dynamics of fcc Yb

The lattice dynamics of fcc Yb at room temperature and atmospheric pressure has been studied by coherent inelastic scattering of neutrons. The phonon dispersion curves were determined along the [$\xi 00$], [$\xi \xi 0$], [$\xi \xi \xi$], and [$0\xi 1$] symmetry directions. The dispersion curves of this divalent element bear a striking resemblance to those of $\gamma$-Ce. In particular, the shear moduli $c_{44}$ and $\frac{1}{2}(c_{11}-c_{12})$ differ by approximately a factor of 4 which implies that fcc Yb (like $\gamma$-Ce) is very anisotropic regarding the propagation of elastic waves. The frequencies of the $T_1\left[\xi \xi 0\right]$ branch for $\xi$ between approximately 0.5 and 0.7 are slightly above the velocity-of-sound line determined from the low-frequency measurements, an anomaly which may be related to the electronic structure of this divalent element. The data were used to evaluate the elastic constants, the phonon density of states, and the lattice specific heat.