Local atomic arrangements close to Ni–25 at.% Pt: Near-surface and bulk microstructure

Diffuse scattering was taken from Ni–23.2 at.% Pt (1 0 0) under grazing incidence at 973 K using photons of 10 keV energy. For comparison, bulk Ni–25.6 at.% Pt was also investigated for a state corresponding to 923 K using Mo Kα radiation. In both cases, the separated short-range order scattering reveals local features of the L12 superstructure – this structure is known for ordered Ni3Pt in the bulk. A much lower degree of local order was found for the (1 0 0) near-surface microstructure than for the bulk, thus suggesting the presence of surface induced disorder. Effective pair interaction parameters determined by the inverse Monte Carlo technique give a dominant nearest-neighbor parameter of ∼46 meV for the near-surface microstructure and ∼80 meV for the bulk. As ∼85 meV was previously noted for Ni–23.2 at.% Pt (1 1 0), the segregation reversal among low-index surfaces seems to be reflected in a different strength for ordering.