Thermodynamic properties of nuclear material uranium carbide using density functional theory

Abstract

To understand the thermal behavior of superhard uranium carbide (UC), in the present work thermodynamic properties of UC in rock-salt structure are investigated using first-principles plane-wave pseudopotential method within the density functional theory. Thermodynamic functions such as specific heat, entropy, internal energy and enthalpy as a function of temperature have been calculated using the phonon dispersion curves and phonon density of states within quasi-harmonic approximation. The variation of lattice specific heat with temperature is also compared with available experimental data. The dependence of selected observations of UC compounds on the effective U parameter has also been investigated. The DFT + U calculation is performed in order to describe precisely the strong on-site Coulomb repulsion incorporation of Hubbard parameter U = 3.0 eV that leads to better comparison of lattice parameter and elastic constants with experimental and available theoretical data. The calculated phonon frequencies and elastic constants show that the UC in rock-salt structure is dynamically and mechanically stable at ambient condition as indicated by their positive values. The temperature dependence of thermal and electrical conductivities has also been calculated and compared with the available experimental data and discussed. The possible use of UC in thermoelectric devices using thermal conductivity and resistivity is also discussed, and the present study suggests that the UC can be a potential candidate for the thermoelectric application at higher temperatures. We hope that the present study should stimulate further studies of this material.