A combined first-principles and experimental study of the lattice site preference of Pt in B2 NiAl

First-principles supercell calculations were undertaken to determine the site preference of Pt in the B2 NiAl lattice structure. The results from these calculations were compared to structural analysis results from high-energy X-ray diffraction experiments. The calculations showed that, at T = 0 K, Pt always has a preference for the Ni sublattice in B2 NiAl, with such a preference being quite strong in Al-rich NiAl, but relatively weak in Ni-rich and stoichiometric NiAl. To predict the site occupation of Pt in B2 NiAl at finite temperatures, a statistical-mechanical Wagner-Schottky model was used in which the formation enthalpies of point defects were determined from the present first-principles calculations. Calculations at T = 1273 K again showed a consistent preference of Pt for the Ni sublattice in Al-rich, Nirich and stoichiometric B2 NiAl. The results from these latter calculations were found to be in very good agreement with those from experiment.