First-principles investigation of intrinsic defects and self-diffusion in ordered phases of V 2 C.

The self-diffusion behavior of vanadium subcarbide (V2 C) is investigated using density functional theory calculations, owing to its potential application as a diffusion barrier in nuclear applications. Three ordered V2 C structures, two of which correspond to experimentally observed phases, are characterized in terms of their equilibrium structural, electronic and elastic properties. Our model for self-diffusion in V2 C considers diffusion of carbon and vanadium to occur separately on each sublattice. Two sets of self-diffusion coefficients are calculated for each structure: one for vacancy-mediated diffusion of vanadium and the other for interstitial diffusion of carbon. Calculated activation energies and diffusion prefactors are compared to experimental data for the cubic transition metal carbides as there is no experimental self-diffusion data for any of the hexagonal subcarbides.