A comparative first-principles study of the electronic, mechanical, defect and acoustic properties of Ti2AlC and Ti3AlC

Ti2AlC and Ti3AlC are both considered as candidate materials for structural applications in harsh environments. In this paper, we adopt density functional theory to study the electronic, elastic, acoustic and defect properties of Ti2AlC and Ti3AlC. It was found that the mechanical properties of Ti2AlC and Ti3AlC vary little; the bulk modulus at equilibrium of Ti3AlC is 10% higher than that of Ti2AlC. However, we found that their defect properties were very different. The migration barrier of an Al vacancy in Ti2AlC is 0.834 eV compared with 4.518 eV in Ti3AlC. The difference by a factor of six in the migration barriers is explained by the bond angle variance of the C-centred octahedral. Using the calculated elastic constants, the slowness surface of the acoustic waves is obtained using the Christoffel equation. Since Ti2AlC and Ti3AlC are often presented as a second Ti-Al-C phase in each other, the individual properties calculated can be used to assess their characterizations in experiments.