First hafnium-based MAX phase in the 312 family, Hf3AlC2: A first-principles study

Abstract

The ground state physical properties of the newly synthesized 312 MAX compound, Hf3AlC2 have been investigated using the first-principles density functional theory (DFT). The optimized unit cell parameters show good agreement with the experimental values. The calculated elastic constants and phonon dispersion confirm the mechanical and dynamical stabilities of this new compound. High bulk modulus, combined with low shear resistance and low Vickers hardness, indicates good machinability of Hf3AlC2, as expected for a metallic compound. On the other hand, significant stiffness due to large Young's modulus as well as the brittle nature according to the calculated Pugh's and Poison's ratios and Cauchy pressure are comparable to that of a ceramic. The present calculations show that Hf3AlC2 is elastically and optically anisotropic. The chemical bonding in Hf3AlC2 consists of a mixture of metallic, covalent and ionic contributions. The calculated Fermi surface contains quasi-two-dimensional topology, which indicates possible superconductivity of Hf3AlC2. The new phase Hf3AlC2 may also be a promising thermal barrier coating (TBC) material. The calculated enthalpy and entropy are found to increase with temperature above 100 K though a decrease is observed for the free energy.