This material was predicted to incorporate Al-vacancies down to a sub-stoichiometry of Ti2Al0.5C. The phase instability beyond a critical Al content was attributed to occupation of the Ti–Al anti-bonding orbital, which reduced the coupling strength between Ti2C slab and Al atomic plane. The migration energy barrier of Al self-diffusion along the (00•1) plane was low, 0.83eV, resulting in rapid out-diffusion of Al during oxidation and decomposition of Ti2AlC at high temperatures.

A First-Principles Investigation of the Phase Stability of Ti2AlC with Al Vacancies. J.Wang, Y.Zhou, T.Liao, J.Zhang, Z.Lin: Scripta Materialia, 2008, 58[3], 227-30

[109] TiC: Point Defects

Here, first-principles calculations were used to elucidate the properties and interactions of TiC point defects and their role in the thermal stability of TiC films. It was found that the stability of defects and defect complexes depended strongly upon structural details. It was also shown, by calculation of diffusion barriers, that while C interstitials were relatively mobile species the migration of C vacancies was suppressed unless the sample was heated to extremely high temperatures. Defect-related effects were considered, and a comparison was made with similar physical traits in transition-metal nitrides.

Vacancies, Interstitials and Their Complexes in Titanium Carbide. L.Tsetseris, S.T.Pantelides: Acta Materialia, 2008, 56[12], 2864-71