  Local fluctuations in the distribution of dopant atoms are a suspected cause
of nanoscale electronic disorder or phase separation observed within the
pnictide superconductors. Atom probe tomography results present the first
direct observations of dopant nano-clustering in a K-doped 122-phase pnictides.
First-principles calculations suggest the coexistence of static magnetism and
superconductivity on a lattice parameter length scale over a large range of
doping concentrations. Collectively, our results provide evidence for a mixed
scenario of phase coexistence and phase separation originating from variation
of dopant atom experiments distroibutions.
