Impact of Defects on Phonon Transport in ThO₂

Defects in ThO2 can significantly degrade the thermal conductivity of ThO2 due to enhanced phonon-defect scattering. In this talk, the impact of point defects, dislocation loops, and grain boundaries are evaluated based on results from non-equilibrium and equilibrium molecular dynamics simulations. Specifically, for point defects, the defect concentration-dependent thermal conductivities are calculated, and these results enable the extraction of phonon-defect scattering cross-section for each type of point defect. Regarding dislocation loops, the impact of two types of experimentally observed dislocation loops (perfect and faulted) is examined considering various loop sizes and orientations. The scattering parameters are deduced based on Klemens’ formalism after the simulation cell size effect is considered. In the case of grain boundaries (GBs), symmetrically tilt GBs are created over a wide range of title angles. The interfacial (Kapitza) resistance is found to correlate well with GB energy. In addition, the spectral/modal analysis of phonon contribution to the total resistance/conductance reveals the dominating phonon modes for thermal transport across GBs.