Narayan Poudel¹, Xiaxin Ding¹, Matthew Mann², Krzysztof Gofryk¹; ¹Idaho National Laboratory, ²Air Force Research Laboratory

Thorium dioxide (ThO2) crystalizes into the CaF2-type cubic structure, similar to other members of the AnO2 (An = Th-Am) family. It forms stoichiometrically and is a wide-gap transparent insulator (Eg~5-6 eV). The thermodynamic and thermal transport properties of ThO2 single crystals have not been studied extensively, especially at low temperatures despite its importance in nuclear fuel technology. Here, we present our detailed measurements of the thermal conductivity, heat capacity, and magnetization of ThO2 single crystals, obtained from room temperature down to 2 K. In this temperature range, many different scattering mechanisms such as boundary, defects, and/or phonon-phonon dominate the heat transport in this material. For these studies, large and good quality single crystals of ThO2 have been synthesized by hydrothermal method. The observed results on ThO2 will be compared with UO2, especially in the context of impact of 5f-electrons on thermodynamic and transport behavior in these materials.