Atomic modelling of carbon atom diffusion in monoclinic zirconia volume, subsurface and surface

Abstract Carbon atom diffusion in monoclinic zirconia from bulk to the ( 1 ¯ 11) surface is studied by Density Functional Theory and atomic Kinetic Monte Carlo (KMC) calculations. The aim is to characterize the behaviour of 14C in one type of nuclear waste in its deep disposal site during a geological timescale at 50 °C. In bulk, diffusion coefficient expression D bulk = 1.6 × 10 − 3 ( cm 2 s ) × e ( − 1.19  eV k B T ) shows a very slow diffusion of 10−22 cm2/s at 50 °C. The carbon atom at the subsurface frontier in the bulk side prefers to diffuse towards the surface rather than staying in the bulk or moving laterally. Diffusion from subsurface to surface is accessible at 50 °C with a minimum migration energy calculated at 0.2 eV. On the surface, diffusion is more probable than in the bulk with a diffusion coefficient expression D s u r f = 1.1 × 10 − 3 ( cm 2 s ) × e ( − 0.76  eV k B T ) equals to 10−15 cm2/s at 50 °C. Atomic KMC simulation shows one dimensional diffusion along an identified path on the surface.