Electronic structure and phase stability of A15 transition metals and alloys

The authors study the electronic structure and the stability of A15 transition metals and alloys at 0K, using a tight-binding approximation and the recursion method. The band contribution to the energy is shown to favour the A15 structure for pure metals when the number of d electrons is about four. This is in agreement with some experimental observations concerning W, Nb, and Cr. Then the energy of formation and the ordering energy of A15 compounds are calculated. They are shown to be quite similar to those of other comparable ordered structures such as the Cu 3 Au (L1 2 ) structure. The relative stability of the A15 and L1 2 structures is studied in some detail. A15 and L1 2 are found to be stable for small and large values of the mean number of d electrons respectively, as is observed experimentally. Finally a general theoretical structural map is presented which accounts for many observed A 3 B transition compounds.