Electronic origin of anomalously high shear modulus and intrinsic brittleness of fcc Ir

Through ab initio density functional theory based calculations, we find that the anomalously large shear modulus and the intrinsic brittleness of face-centred cubic (fcc) iridium (Ir) are primarily a consequence of its relatively strong bonds. Comparative analysis of the bond order, which dictates the bond strength, the localization of the valence electrons and the elastic constants of Ir and a selection of fcc metals allows us to rationalize the peculiarities of Ir in terms of its strong and directional bonds. Furthermore, the similarities between the failures of Al and Ir are suggested to reflect the resemblance existing between the angular features of their bonds.