A series of Al-25 (Nb,Sc), at.%, and Al-25 (Zr,Sc), at.%, alloy buttons were arccast in argon and homogenized for 2 h in vacuum at temperatures ranging from 1473 to 1573K. X-ray powder-diffraction indicated that almost all the Nb in Al-25 Nb (DO22) had to be replaced by Sc in order to obtain the Ll2 structure. In the case of Al3Zr much less Sc was required - the single phase Ll2 composition is approximately Al16Zr8Sc.
Recent calculations [1,2] show that once the tetragonality is properly included the phase stability of the trialuminide transition-metal binary alloys can be understood in terms of their electronic density of states. The dominating feature is a deep minimum in the density of states just below the major transition metal d-band peak. The exact position of the minimum changes with structure type (i.e., Ll2, DO22, or DO23, and with c/a). The alignment of the Fermi energy with the minimum appears to determine the equilibrium structure. The results of linearized-muffin-tin-orbital  (LMTO) electronic structure calculations are compared to the rigid band model and checked against the experimentally determined phase boundaries.