Direct observation of local K variation and its correlation to   electronic inhomogeneity in (Ba1-xKx)Fe2As2 Pnictide
  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. 
W. K. Yeoh, B. Gault, X. Y. Cui, C. Zhu, M. P. Moody, L. Li, R. K.   Zheng, W. X Li, X. L. Wang, S. X. Dou, C. T. Lin and S....
cond-mat.supr-con