Phase stability of the intermetallic compound Al Nb 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 Al Ni Nb compounds (where n is an integer from 0 to 6) are calculated for both D0 and Ll 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 D0 structure is stable in the binary Al Nb compound as compared with the Ll structure; conversely, the L 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 D0 and Ll are — 0.79 eV and 0.56 eV for n equal to 0 and 2, respectively. © 1991 Taylor & Francis Group, LLC.