  The superconducting (SC) phase in the phase-separated (PS) K0.8Fe1.6+xSe2
(0<=x<=0.15) materials is found to crystallize on Archimedean solid-like
frameworks, this structural feature originate from a spinodal phase separation
(SPS) at around Ts~540K depending slightly on the Fe concentration. Two stable
phases in K0.8Fe1.6+xSe2 are demonstrated to be the SC K0.5Fe2Se2 and
antiferromagnetic (AFM) K0.8Fe1.6Se2. The spinodal waves go along the
systematic [113] direction and result in notable lamellar structure as
illustrated by using the strain-field theoretical simulation. The 3-dimentional
SC framework is constructed by hollow truncated octahedra similar with what
discussed for Archimedean solids. Based on this structural model, we can
efficiently calculate the volume fraction of SC phase in this type of PS SC
materials.
