  Structural investigations on the K0.8Fe1.6+xSe2 superconducting materials
have revealed remarkable micro-stripes arising evidently from the phase
separation. Two coexisted structural phases can be characterized by modulations
of q1 = 1/5[a*+3b*], the antiferromagnetic phase K0.8Fe1.6Se2, and q2 =
1/2[a*+b*], the superconducting phase K0.75Fe2Se2, respectively. These stripe
patterns likely result from the anisotropic assembly of superconducting
particles along the [110] and [1-10] direction. In addition to the notable
stripe structures, a nano-scale phase separation also appears in present
superconducting system as clearly observed by high-resolution transmission
electron microscopy. Certain notable experimental data obtained in this
heterogenous system can be quantitatively explained by the percolation
scenario.
