Phase stability of Al3Nb as a function of nickel additions

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Abstract
Phase stability of the intermetallic compound Al3Nb is investigated as a function of nickel additions by band structure calculations based on an extended Hueckel tight-binding method. With this method, the electronic structure and total energies of the Al6-n -Ni n Nb2 compounds (where n is an integer from 0 to 6) are calculated for both D022 and L12 structures under the assumption that nickel substitutes for aluminium. The electronic total energies obtained from integration of the energy states of all electrons considered have shown that the D022 structure is stable in the binary Al3Nb compound as compared with the L12 structure; conversely, the L12 structure is stable for compounds with n values greater than 1. These calculations are in good agreement with X-ray diffraction results reported by Schubert and co-workers. Differences in the electronic total energy per atom between D022 and L12 are - 0·79 eV and 0·56 eV for n equal to 0 and 2, respectively.