Max phases and mxenes

MAX phases and their two-dimensional siblings MXenes are large, and rapidly growing, classes of materials, that present a huge playground for theoretical and experimental (inorganic) chemists and transcend into multiple adjacent disciplines, such as materials science, solid-state physics, engineering, molecular chemistry and biomedicine. More than 155 MAX phases—layered ternary carbides or nitrides (e.g., Ti2SiC, Cr2AlN), that crystallize in a hexagonal crystal structure—have been synthesized so far and more combinations of early transition metals (M), main group elements (A), and carbon/nitrogen or both have theoretically been predicted (either as ternary compounds or quaternary solid solutions). This invites extensive and diverse activities in the field of materials syntheses, which enable the preparation of new members of the MAX phase family, lead to innovative processing methods to achieve clever MAX phase microstructures and morphologies, and with that open up the path to new functionalities of these metallic ceramics/ceramic metals. Furthermore, they are the precursor for their 2D analogs (MXenes), that are obtained by selective removal of the A element (mostly Al and Ga) and subsequent delamination of the atomically-thin carbide/nitride sheets. Due to their 2D nature, MXenes exhibit many similarities to graphene while being conductive, mechanically robust, and chemically more flexible.