Crystal Structure and Elastic Properties of Hypothesized MAX Phase‐Like Compound (Cr2Hf)2Al3C3

The term “ MAX phase” refers to a very interesting and important class of layered ternary transition‐metal carbides and nitrides with a novel combination of both metal and ceramic‐like properties that have made these materials highly regarded candidates for numerous technological and engineering applications. Using ( Cr 2 Hf ) 2 Al 3 C 3 as an example, we demonstrate the possibility of incorporating more types of elements into a MAX phase while maintaining the crystallinity, instead of creating solid solution phases. The crystal structure and elastic properties of MAX phase‐like ( Cr 2 Hf ) 2 Al 3 C 3 are studied using the Vienna ab initio Simulation Package. Unlike MAX phases with a hexagonal symmetry ( P 6 3 / mmc , #194), (Cr 2 Hf) 2 Al 3 C 3 crystallizes in the monoclinic space group of P 2 1 / m (#11) with lattice parameters of a = 5.1739 Å, b = 5.1974 Å, c = 12.8019 Å; α = β = 90°, γ = 119.8509°. Its structure is found to be energetically much more favorable with an energy (per formula unit) of −102.11 eV, significantly lower than those of the allotropic segregation (−100.05 eV) and solid solution (−100.13 eV) phases. Calculations using a stress versus strain approach and the VRH approximation for polycrystals also show that ( Cr 2 Hf ) 2 Al 3 C 3 has outstanding elastic moduli.