First-principles study of thermophysical properties of uranium dioxide

Highlights: • Thermophysical properties of UO₂ were systematically studied by DFT+U method. • The thermodynamic properties of UO₂ can be well described by quasiharmonic approximation under 1000 K. • Phonon scatterings by defects in UO₂ are critical at room temperature. - Abstract: The structural and elastic properties, lattice dynamics and thermophysical properties of uranium dioxide (UO₂) were studied by DFT based first-principles calculations. LDA+U method shows the overall best description of the lattice parameters and elastic constants of UO₂ among all the DFT methods studied. The phonon dispersion relations of UO₂ predicted by direct method agree with experimental results. Thermodynamic properties, including Gibbs energy, enthalpy, entropy and heat capacity, were evaluated under quasiharmonic approximation using the calculated phonon density of states. Good agreement with experiments is obtained up to 1000 K. Further improvement of heat capacity at high temperatures can be achieved by taking into account of thermal expansion. The calculated lattice thermal conductivity of UO₂ shows that phonon scatterings by defects are critical at room temperature while three-phonon interactions dominate the phonon scattering at high temperatures