Iridium concentration driving the mechanical properties of iridium–aluminum compounds

Abstract

Using first-principles density functional theory approach, we systematically investigate the formation enthalpy, mechanical stability, elastic modulus, brittle or ductile behavior and electronic structure of Ir–Al compounds with different Ir concentrations. The calculated convex hull indicates that IrAl with CsCl-type structure is more stability than that of other Ir–Al compounds at ground state. We found that the resistance to volume deformation is related to the Ir concentration in Ir–Al compounds, while the bulk modulus of these compounds increases with increasing Ir concentrations. However, the Ir5Al3 has the strongest shear deformation resistance and has the highest elastic stiffness in these Ir–Al compounds. The calculated theoretical hardness of Ir2Al9 is bigger than other Ir–Al compounds. Ir2Al3 and Ir2Al9 exhibit brittle behavior in contrast to other Ir–Al compounds exhibit ductile behavior. This discrepancy is originated from the structural feature and localized hybridization between Ir and Al atoms. Finally, we conclude that alloying can change brittle behavior of metal Ir.