Benefits of oxygen incorporation in atomic laminates

  • Dahlqvist, Martin
Atomic laminates such as MAX phases benefit from the addition of oxygen in many ways, from the formation of a protective oxide surface layer with self-healing capabilities when cracks form to the tuning of anisotropic conductivity. In this paper oxygen incorporation and vacancy formation in M 2 AlC ( M   =  Ti, V, Cr) MAX phases have been studied using first-principles calculations where the focus is on phase stability and electronic structure for different oxygen and/or vacancy configurations. Oxygen prefers different lattice sites depending on M -element and this can be correlated to the number of available non-bonding M d -electrons. In Ti 2 AlC, oxygen substitutes carbon while in Cr 2 AlC it is located interstitially within the Al-layer. I predict that oxygen incorporation in Ti 2 AlC stabilizes the material, which explains the experimentally observed 12.5 at% oxygen ( x   =  0.5) in Ti 2 Al(C 1− x O x ). In addition, it is also possible to use oxygen to stabilize the hypothetical Zr 2 AlC and Hf 2 AlC. Hence, oxygen incorporation may be beneficial in many ways. Not only can it make a material more stable, but it also can act as a reservoir for internal self-healing with shorter diffusion paths.
Type of Publication:
Journal of Physics: Condensed Matter