Thermodynamic and mechanical stabilities of γ′-Ir₃ (Al,W)

The structural, thermodynamic, and mechanical properties of a recently identified γ′ -Ir₃ (Al,W) compound are investigated using first-principles density functional calculations. The configurational disorder in this compound is treated by both the special quasirandom structure approach and the cluster expansion technique, and the two complimentary methods give results in excellent agreement with each other. In support of experiments, our T=0 K calculations indicate that γ′ -Ir₃ (Al _1-x W_x) is thermodynamically stable in the Ir-Al-W ternary system over a limited composition range near x=0.5. At finite temperatures, γ′ -Ir₃ (Al,W) will be further stabilized by configurational and vibrational entropies but will be slightly destabilized due to thermal electronic excitations. The single-crystal elastic constants of γ′ -Ir₃ (Al,W) are obtained using an efficient stress-strain approach. We find that the alloying of W in γ′ -Ir₃ (Al,W) significantly enhances its strength, although at the cost of reduced ductility due to the directionality of atomic bonding between Ir and W atoms.