Using a novel many-body approach, we report lattice dynamical properties of ${\mathrm{UO}}_2$ and ${\mathrm{PuO}}_2$ and uncover various contributions to their thermal conductivities. Via calculated Grüneisen constants, we show that only longitudinal acoustic modes having large phonon group velocities are efficient heat carriers. Despite the fact that some optical modes also show their velocities which are extremely large, they do not participate in the heat transfer due to their unusual anharmonicity. Ways to improve thermal conductivity in these materials are discussed.

• Received 14 February 2008

DOI:https://doi.org/10.1103/PhysRevLett.100.225504