Expanding the elemental space of atomic laminates by a theoretical/experimental approach

More than 50 years ago a family of atomically laminated compounds were discovered, being comprised of a transition metal M, an A-group element, and carbon and/or nitrogen X, and therefore being referred to as MAX phases. The exploration of the taxonomy of these can be accelerated by theoretical design on the atomic level combined with combinatorial experimental synthesis. Here, we use predictive phase stability calculations to probe transition metal (M) alloying in MAX phases and identify several chemically ordered structures. Subsequent materials synthesis of these indicates a potentially large family of thermodynamically stable phases, with Kagomé-like and in-plane chemical ordering, and with incorporation of elements previously not used for MAX phases, including Y and W. In extension, we suggest a matching set of novel two-dimensional MXenes, from selective etching of the A-element and, when so required, the alloying metal. The here demonstrated structural design on both 3D and 2D atomic levels expands the property tuning potential of functional ceramics.