An ab initio study on the investigation of structural, electronic, mechanical and lattice dynamical properties of the M2AX type MAX phases Sc2AlB0.5C0.5, Sc2AlB0.5N0.5 and Sc2AlC0.5N0.5 compounds

Abstract

The hypothetical Sc2AlB0.5C0.5, Sc2AlB0.5N0.5 and Sc2AlC0.5N0.5 compounds are M2AX type MAX phases referred to as #211 and have hexagonal crystal structure which conforms to P63/mmc space group. These compounds have been investigated by using generalized gradient approximation in the Density Functional Theory and plane-wave pseudopotential method. After the optimization process of the compounds, their structural, electronic, mechanical, and lattice dynamical properties have been examined in detail. The calculated electronic band structure and the total electronic density of states indicated that all of our compounds have metallic behavior. The estimated elastic constants show that they are stable and have anisotropic character mechanically. Moreover, Sc2AlB0.5C0.5 and Sc2AlB0.5N0.5 are ductile, while Sc2AlC0.5N0.5 is brittle. Also, the obtained phonon dispersion curves indicate that Sc2AlC0.5N0.5 is stable, whereas Sc2AlB0.5C0.5 and Sc2AlB0.5N0.5 compounds are dynamically unstable with imaginary vibrational modes.