Abstract
The electronic structure of NiAl with non-stoichiometric defects was investigated using the discrete variational (DV)-Xα cluster calculation. On the nickel-rich side of stoichiometry the defect is a substitutional nickel atom on the aluminium sublattice which modifies the electron density of states. This modification is mainly due to the appearance of d levels of the substitutional nickel atom below the Fermi level E f . On the aluminium-rich side nickel vacancies are formed which lead to vacancy levels (or a band) below E f which originate from the 3d orbitals of the nickel neighbours of these vacancies. The ionicity of the atoms near the defect and the bond order between the atoms also change with the non-stoichiometry. NiAl appears to be most stable at the stoichiometric composition and becomes increasingly unstable with increasing defect concentration. The types of defect which produce the smallest changes in the charge distribution seem to be introduced preferentially into non-stoichiometric NiAl.
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