  A metastable {\epsilon}-Al60Sm11 phase appears during the initial
devitrification of as-quenched Al-10.2 at.% Sm glasses. The {\epsilon} phase is
nonstoichiometric in nature since Al occupation is observed on the 16f Sm
lattice sites. Scanning transmission electron microscopic images reveal
profound spatial correlation of Sm content on these sites, which cannot be
explained by the "average crystal" description from Rietveld analysis of
diffraction data. Thermodynamically favorable configurations, established by
Monte Carlo (MC) simulations based on a cluster-expansion model, also give
qualitatively different correlation functions from experimental observations.
On the other hand, molecular dynamics simulations of the growth of
{\epsilon}-Al60Sm11 in undercooled liquid show that when the diffusion range of
Sm is limited to ~ 4 {\AA}, the correlation function of the as-grown crystal
structure agrees well with that of the STEM images. Our results show that
kinetic effects, especially the limited diffusivity of Sm atoms plays the
fundamental role in determining the nonstoichiometric site occupancies of the
{\epsilon}-Al60Sm11 phase during the crystallization process.
