Mekhed A. Structural-phase state and properties of Fe-Al-C alloys with non-stoichiometric carbide phase

The present work is dedicated to the study of the non-stoichiometric K-phase using density-functional theory as implemented in WIEN2k package. It was established that degenerate electron states at the Fermi level make stoichiometric K-phase susceptible to a symmetry degenerating deformations. Non-stoichiometry by carbon increases stability of a unit cell as a whole due to delocatization of electronic states densities of iron and carbon atoms and due to appearance of new states at -7 - -6 eV which increases the strength of Fe-C bonds, while non-stoichiometry by aluminum weakens Fe-C bonds. It was established that Fe3AlC0.66 composition has the minimal value of formation enthalpy and the difference of formation enthalpy of various compounds was as high as 40%. Unit cell parameters of magnetic K-phase varied between 0.372 to 0.375 nm and were smaller by 0.4-0.8% comparing to stoichiometric one. Magnetization value of non-stoichiometric Fe3AlC0.66 compound was the closest to the experimental one. The possibility of epitaxial growth of diamond crystals on K-phase substrate was shown. (200) plane was established to be the most suitable plane for the diamond growth. The electron structure and energetic parameters of a substrate was investigated. It was shown that the substrate with at least four intermediate layers of K-phase exhibits signs of stability such as negative enthalpy of formation and Fermi level falling on minimum of densities of states.