Stability and formation pathways of compositionally complex M-layer MAX phases

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ABSTRACT MAX phases exhibit unusual combinations of metallic and ceramic properties and offer broad opportunities to tailor those properties through incorporation of multiple elements on the M, A, and X sites. However, conventional synthesis from elemental or binary powders often involves complex reaction pathways, intermediate phase formation, competing reactions, and deviations from targeted stoichiometry. Here, we synthesize 26 targeted M 2 AlC compositions containing two to five equiatomic M-site elements using high-purity single-element MAX phase precursors (T 2 AlC, Ta 2 AlC, V 2 AlC, Nb 2 AlC, and Cr 2 AlC). This approach minimizes intermediate-phase formation and promotes solid-solution formation. Coupling experimental results with composition-based machine learning analysis reveals that only nine compositions form phase-pure M 2 AlC phases, while the remaining compositions produce non-targeted chemistries, competing phases, or undergo decomposition upon cooling. The observed phase-formation behavior correlates strongly with a coupled geometric–electronic balance, providing a data-driven framework for assessing phase-stability trends and supporting future predictive screening of multicomponent MAX-phase chemistries.

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