Coexistence of different electronic phases in the K0.8Fe1.6Se2   superconductor: a bulk-sensitive hard x-rays spectroscopy study
  We have studied electronic and magnetic properties of the K0.8Fe1.6Se2 superconductor by x-ray absorption and emission spectroscopy. Detailed temperature dependent measurements alongwith a direct comparison with the binary FeSe system have revealed coexisting electronic phases: a majority phase with high spin 3+Fe state and a minority phase with intermediate spin 2+Fe state. The effect of high temperature annealing suggests that the compressed phase with lower spin 2+Fe state is directly related with the high Tc superconductivity in the title system. The results clearly underline glassy nature of superconductivity in the electronically inhomogeneous K0.8Fe1.6Se2, similar to the superconductivity in granular phases. 
L. Simonelli, N. L. Saini, M. Moretti Sala, Y. Mizuguchi, Y. Takano,   H. Takeya, T. Mizokawa, and G. Monaco
cond-mat.supr-con