Phonon density of states in uranium Laves phases UNi2 and UCo2

Abstract

Recent computational work evaluated the phase stability of UCo2 and UNi2 in the C14, C15, and C36 Laves phases and reported their computationally determined phonon density of states. To corroborate these computational findings, we report the experimentally determined phonon density of states for UCo2 and UNi2 using inelastic neutron scattering at the wide angular-range chopper spectrometer at the Spallation Neutron Source at Oak Ridge National Laboratory. We found excellent agreement between experimental and computational results for UNi2 and noted that some differences were observed for UCo2. By comparing the phonon density of states of UCo2 with that of other U-bearing Laves phases, we found that UCo2 showed distinct vibrational properties. From the one-phonon density of states, we calculated the lattice contribution to the specific heat of UNi2 and UCo2. Finally, we bound the electronic contribution to the specific heat in UNi2.