First-principles investigation of the Ni-Fe-Al system

By combining ab initio electron theory and statistical mechanics, the physical properties of the ternary intermetallic system Ni-Fe-Al in the ground state and at finite temperatures were investigated. The Ni-Fe-Al system is not only of high technological interest, but exhibits also rich physics, e.g. a delicate interplay between structure and magnetism over a wide composition range and substantial electronic correlations which is challenging for modern electronic structure methods. The new Stuttgart ab initio mixed-basis pseudopotential code in the generalized gradient approximation (GGA) was used to determine the energetics in the ground state. Therewith, in combination with the cluster expansion (CE) method a representation of the energy landscape at T=0 over the whole Gibbs triangle was elaborated. At finite temperatures, the cluster variation method (CVM) in tetrahedron approximation was employed in order to calculate the ab initio ternary phase diagram on the bcc and fcc lattice. Thereby, a miscibility gap in the ternary B2 phase was theoretically verified.