Mechanical behavior, bonding nature, and defect processes of Mo2ScAlC2: a new ordered MAX phase

Abstract: In the present study we employed density functional theory calculations to investigate the mechanical behavior, bonding nature and defect processes of the new ordered MAX phase Mo2ScAlC2. The mechanical stability of the compound is verified with its single crystal elastic constants. The new phase Mo2ScAlC2 is anticipated to be prone to shear along the crystallographic b and c axes, when a rational force is applied to the crystallographic a axis. The compressibility along the <001> direction under uniaxial stress is expected to be easier in Mo2ScAlC2. Additionally, the volume deformation should be easier in Mo2ScAlC2 than in the isostructural Mo2TiAlC2. Mo2ScAlC2 is predicted to behave in a brittle manner. Due to its higher Debye temperature, Mo2ScAlC2 is expected to be thermally more conductive than Mo2TiAlC2. The cross-slip pinning procedure should be significantly easier in Mo2ScAlC2 as compared to Mo2TiAlC2. The new ordered MAX phase Mo2ScAlC2 has a mixed character of strong covalent and metallic bonding with limited ionic nature. Both Mo-C and Mo-Al bonds are expected to be more covalent in Mo2ScAlC2 than those of Mo2TiAlC2. the level of covalency of Sc-C bond is somewhat low compared to a similar bond Ti-C in Mo2TiAlC2. Due to its reduced hardness, Mo2ScAlC2 should be softer and more easily machinable compared to Mo2TiAlC2. Fermi surface topology of the new compound is formed mainly due to the low-dispersive Mo 4d-like bands. The intrinsic defect processes reveal that the level of radiation tolerance in Mo2ScAlC2 is not as high as in other MAX phases such as Ti3AlC2.