An investigation of the in-plane chemically ordered atomic laminates (Mo2/3Sc1/3)2AlC and (Mo2/3Y1/3)2AlC from first principles

Abstract

We have calculated electronic, vibrational, and elastic properties of (Mo_2/3Sc_1/3)₂AlC and (Mo_2/3Y_1/3)₂AlC, two recently discovered nanolaminated materials in the family of so-called i-MAX phases. A comparison is made to the properties of the related hypothetical MAX phases Sc₂AlC, Y₂AlC, and Mo₂AlC. From an analysis of the electronic band structures and projected crystal orbital Hamilton populations (pCOHP), we show that the i-MAX phases have more isotropic band structures than the MAX phases, but that their bonding characteristics are very similar, despite belonging to different space groups. However, the similar bonding notwithstanding, qualitative as well as significant quantitative differences are seen in the phonon density of states (PDOS). We also compare the Voigt–Reuss–Hill (VRH) bulk, shear, and Young's moduli. For (Mo_2/3Sc_1/3)₂AlC, B_VRH = 132 GPa, G_VRH = 89 GPa, and E_VRH = 218 GPa, all of which are higher values than for Sc₂AlC, but lower than for Mo₂AlC. For (Mo_2/3Y_1/3)₂AlC, B_VRH = 117 GPa, G_VRH = 85 GPa, and E_VRH = 205 GPa, which are higher than for Y₂AlC, but lower than for Mo₂AlC.