  Atomic scale x-ray photon correlation spectroscopy (aXPCS) was used to study
atomic diffusion in the Ni97 Pt3 solid solution with both a single crystal and
a polycrystalline sample. Different jump diffusion models are discussed using
experimental results and Monte Carlo simulations. The sensitivity of aXPCS
experiments to short-range order (in this case governed by a strong Pt-Pt
repulsive force) is demonstrated. The activation energy of 2.93(10) eV as well
as diffusivities in the range of 10-23 m2 s-1 at 830 K agree very well with the
results of tracer diffusion studies at much higher temperatures.
