Ab initio modeling of MAB phase solid solutions

MAB phases are layered ternary or quaternary compounds, where M stands for a transition metal element. A indicates a group III-A or IV-A element, and B is boron. MAB structures are composed of M-B sublattices interleaved by A-atom mono- or bilayers. MAB phases are technologically important materials exhibiting both metallic and ceramic properties. MAB phases crystallize in different crystal structures depending on the composition. Such diversity of crystal structures strongly suggests that MAB phases' properties are tunable through the crystal structure and compositional control. Tuning the chemical composition offers an additional degree of freedom in the quest for stable materials with physical and chemical properties appealing for both fundamental research and technological applications. In this respect, we investigated the phase stability of MAB phase solutions by mixing two different transition metal elements using, density functional calculations, cluster expansion, and special quasirandom structure approach. We elucidated the mixing thermodynamics of different transition metal atoms in MAB solid alloy solutions. We determined the alloying behaviors, namely (1) an ordering tendency to form ordered structures, (2) a clustering tendency to form phase separation, and (3) a mixing tendency to form disordered alloy structures. We discussed the material properties of the predicted MAB solid solutions.