Electronic structure, bonding characteristics, and mechanical properties in (W 2/3 Sc 1/3 ) 2 AlC and (W 2/3 Y 1/3 ) 2 AlC i-MAX phases from first-principles calculations.

With the recent discovery of in-plane chemically ordered MAX phases (i-MAX) of the general formula ([Formula: see text])2 AC comes addition of non-traditional MAX phase elements. In the present study, we use density functional theory calculations to investigate the electronic structure, bonding nature, and mechanical properties of the novel (W2/3 Sc1/3 )2 AlC and (W2/3 Y1/3 )2 AlC i-MAX phases. From analysis of the electronic structure and projected crystal orbital Hamilton populations, we show that the metallic i-MAX phases have significant hybridization between W and C, as well as Sc(Y) and C states, indicative of strong covalent bonding. Substitution of Sc for Y (M 2 ) leads to reduced bonding strength for W-C and Al-Al interactions while M 2 -C and M 2 -Al interactions are strengthened. We also compare the Voigt-Reuss-Hill bulk, shear, and Young's moduli along the series of M 1   =  Cr, Mo, and W, and relate these trends to the bonding interactions. Furthermore, we find overall larger moduli for Sc-based i-MAX phases.