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