Lattice dynamics and lattice thermal conductivity of thorium dicarbide

The elastic and thermodynamic properties of ThC₂ with a monoclinic symmetry have been studied by means of density functional theory and direct force-constant method. The calculated properties including the thermal expansion, the heat capacity and the elastic constants are in a good agreement with experiment. Our results show that the vibrational property of the C ₂ dimer in ThC₂ is similar to that of a free standing C₂ dimer. This indicates that the C₂ dimer in ThC ₂ is not strongly bonded to Th atoms. The lattice thermal conductivity for ThC₂ was calculated by means of the Debye-Callaway model. As a comparison, the conductivity of ThC was also calculated. Our results show that the ThC and ThC₂ contributions of the lattice thermal conductivity to the total conductivity are 29% and 17%, respectively.