Effects of 4d transition metals on NiAl bonds characters from first principles

We study systematically the site occupancy and effects of alloying element on NiAl bonds character of 4d transition metals by first-principles method based on density functional theory. The impurity formation energies of 4d TM of NiAl in Al-site and Ni-site are calculated. Y, Zr, Nb, Cd prefer to occupy the Al-site, whereas Mo, Tc, Ru, Rh, Pd, Ag prefers to occupy Ni-site. Crystal distortion and the overlap population between the alloying element and its first-neighboring atoms and are also calculated. The result shows that the substituting Al-site the elements Y, Zr, Nb, Cd interact with its first-neighboring Ni atom by anti-bonding. The total covalent ratio is decreased by theses elements which may improve ductility of NiAl. For Ni-site elements, the interaction between the alloying element Mo (Tc, Ru, Rh, Pd, and Ag) with its first-neighboring atoms Al also shows decrease in covalent. Site occupation of 4d transition metals are also discussed by the reaction energy for formation Ni₂TiX and X bulk phase.