We present first-principles calculations of the structural and electronic p
roperties of orthorhombic NiAl3, including the intrinsic point defects. The
energies obtained from these calculations are employed in a statistical me
chanics model to investigate the role of NiAl3 in the Ni-Al phase diagram.
Our calculations show that the preferred constituent defect mechanisms for
NiAl3 off stoichiometry are the 8d Ni antisites on the Ni-rich side and Ni
vacancies on the Al-rich side. The calculated free energy is in agreement w
ith the observation that NiAl3 is a stoichiometric compound.