Energetics of point defects in TiC

摘要

Density functional theory was used to evaluate the energetics of point defects in TiC_x (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 TiC_x and the subsequent formation of Ti_3AlC_2. 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(l 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 Ti_3AlC_2 is formed by Al surface ingress into TiC_x and that vacancy ordering takes place.