First-principles investigation of the anomalous carbon diffusion in TiC0.67

Abstract

In this work, we address a long-standing question about the link between vacancy order–disorder transitions and carbon diffusion activation energy in substoichiometric titanium carbide. This is accomplished using Monte Carlo and kinetic Monte Carlo simulations with energetics informed by the cluster expansion method to determine equilibrium order parameter and interstitial diffusion rates as a function of simulation temperature. Since all the data for these models come from density functional theory, these predictions represent first-principles predictions of these properties. From the simulation results, we conclude that the energetic preference to remain in an ordered configuration promotes correlated diffusion, resulting in an increased carbon diffusion activation energy at temperatures below the order–disorder transition temperature. Furthermore, the change in activation energy appears to be correlated with the change in short-range order.