Impact of small defects and dislocation loops on phonon scattering and thermal transport in ThO₂

Radiation damage can significantly degrade the thermal conductivity of ThO₂ due to enhanced phonon-defect scattering. To quantify the effect of radiation-induced defects on thermal transport, we employ non-equilibrium molecular dynamics simulations to estimate the thermal conductivity in the presence of various types of defects. For each defect species, the phonon-defect scattering cross-section is extracted based on analytical models. In addition, the impact from two types of experimentally-observed dislocation loops (perfect and faulted) on thermal transport is examined with respect to the loop size and orientation. Notably, simulation cell size effects are analytically and quantitatively addressed via a phonon-mean-free-path-resolved analysis. It can be concluded that, for a given total number of defect sites per unit volume, agglomerating defects into larger clusters improves thermal conductivity compared to isolated defects. Importantly, this work provides quantitative information towards the defect-specific thermal conductivity, and phonon-defect scattering cross-sections, which can serve as inputs to large-scale transport models to quantify the evolution of overall thermal conductivity of ThO₂ under irradiation.