Predictive theoretical screening of phase stability for chemical order and disorder in quaternary 312 and 413 MAX phases

Abstract

In this work we systematically explore a class of atomically laminated materials, Mn+1AXn (MAX) phases upon alloying between two transition metals, M′ and M′′, from groups III to VI (Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W). The materials investigated focus on so called o-MAX phases with out-of-plane chemical ordering of M′ and M′′, and their disordered counterparts, for A = Al and X = C. Through use of predictive phase stability calculations, we confirm all experimentally known phases to date, and also suggest a range of stable ordered and disordered hypothetical elemental combinations. Ordered o-MAX is favoured when (i) M′ next to the Al-layer does not form a corresponding binary rock-salt MC structure, (ii) the size difference between M′ and M′′ is small, and (iii) the difference in electronegativity between M′ and Al is large. Preference for chemical disorder is favoured when the size and electronegativity of M′ and M′′ is similar, in combination with a minor difference in electronegativity of M′ and Al. We also propose guidelines to use in the search for novel o-MAX; to combine M′ from group 6 (Cr, Mo, W) with M′′ from groups 3 to 5 (Sc only for 312, Ti, Zr, Hf, V, Nb, Ta). Correspondingly, we suggest formation of disordered MAX phases by combing M′ and M′′ within groups 3 to 5 (Sc, Ti, Zr, Hf, V, Nb, Ta). The addition of novel elemental combinations in MAX phases, and in turn in their potential two-dimensional MXene derivatives, allow for property tuning of functional materials.