Thermal conductivity of ultra high temperature ceramics (UHTC) $ZrB_2$ and $HfB_2$ from atomistic simulations

Ultra high temperature ceramics (UHTC) including $ZrB_2$ and $HfB_2$ are characterized by high melting point, good strength, and reasonable oxidation resistance. These materials are of interest for use as sharp leading edges for hypersonic vehicles among other applications. Progress in computational modeling of UHTCs has been limited in part due to the absence of suitable interatomic potentials. Recently, we developed Tersoff style parametrizations of such potentials for both $ZrB_2$ and $HfB_2$ appropriate for atomistic simulations. As an application, Green-Kubo molecular dynamics simulations were performed to evaluate the lattice thermal conductivity for single crystals of $ZrB_2$ and $HfB_2$. The atomic mass difference in these binary compounds leads to oscilations in the time correlation function of the heat current, in contrast to the more typical monotonic decay seen in monoatomic materials. Results at room temperature and at elevated temperatures will be reported.