Transition-metal aluminide formation: The 4d aluminides

The heats of formation for ordered binary 4d transition-metal (Y and Nb-Pd) aluminides are calculated from first-principles for different compositions and for a number of competing crystal structures. The calculated heatsfor these aluminides are typically within ∼0.01 eV/atom of the calorimetric values, faithfully tracing the trends in alloying for diverse crystalline packings, with the maximum heat of formation associated with RhAl. Issues of the stability versus the metastability of several reported phases are addressed.