M_n+1AX_n

The MAX phases are made up of an early transition metal M (red), an element from the A groups, usually IIIA and IVA (blue), and a third element, X, which is either nitrogen or carbon (black), in the composition M_n+1AX_n, where n is 1, 2 or 3. The classes of materials characterized to date naturally form into three groups, based on the number of atoms of the M, A and X elements in each molecule; these groups are known as 211, 312 and 413 materials. To date, more than 50 MAX phases are known.