Energetics of point defects in TiC

Density functional theory was used to evaluate the energetics of point defects in TiCx (x < 1): C vacancies and Al substitution at a C site. Our ambition is to contribute towards understanding the underlying atomic mechanisms enabling the Al intercalation into TiCx and the subsequent formation of Ti3AlC2. The difference between the energy of formation for an Al substitution at a C site and a bulk C vacancy is 0.224 eV. Furthermore, only 49 meV/vacancy is required to order the existing bulk C vacancies. Surface effects were also considered: the energy of formation for Al on TiC(1 0 0) at a vacant surface C site is smaller by 2.779 eV than in the case of the C surface vacancy, indicating that Al is likely to be incorporated. Based on these energy differences, it is reasonable to assume that Ti3AlC2 is formed by Al surface ingress into TiCx and that vacancy ordering takes place.