A field ion microscope investigation of short-range order in 2a/oAu–Pt and 2a/oNi–Pt

A field ion microscope study has directly revealed the positions of solute atoms in the solid solutions of 2a/o Ni–Pt and 2a/o Au–Pt. Analysis of these data has yielded Warren short-range order coefficients, cluster distribution functions and the morphology of the clusters. Nearest-neighbour clusters are found in the Au–Pt solution: the reverse tendency (ordering) is found in the Ni–Pt solution. The clusters found in 2a/o Au–Pt are planar and predominantly along (111). Interaction energies have been calculated using α1 values and the quasi-chemical approximation. Values of +915 ± 120 cal/mole and -760 ± 280 cal/mole have been obtained for the Au–Pt and Ni–Pt solutions, respectively. These values are in good agreement with values derived from thermochemical data.