Ternary transition-metal aluminide alloy formation: The ${\mathrm{BiF}}_3$ structure

Almost 50 ternary transition-metal aluminides have been reported in the ordered ${\mathrm{BiF}}_3$ structure, representing roughly half of the observed ordered ternaries. To investigate the possible occurrence of other aluminides in this structure, the heats of formation of 38 ordered ${\mathrm{M}}_2\mathrm{NAl}$ ternaries, most not reported to occur, have been calculated. While all but one is stable relative to the elemental metals, the test for ternary stability requires comparison of the ternary heat with competing two and three phase mixtures of binary phases. Of the ${\mathrm{BiF}}_3$ ternaries hitherto unreported, nine are estimated to occur while eighteen are found to be unstable. The pattern of occurrence obtained from experiments and calculations taken together suggests that on the order of another 20 compounds beyond those predicted here could exist. Thus, this important ordered phase is more pervasive than previously suggested by experiment.