K<sub<2</sub<Fe<sub<7</sub<Se<sub<8</sub<：A possible parent phase for superconductivity in iron-based material K<sub<x</sub<Fe<sub<2-y</sub<Se<sub<2</sub<

The search for new superconducting materials has been spurred on by the discovery of iron-based superconductors whose structure and composition is qualitatively different from the cuprates. The study of one such material，K<sub<x</sub<Fe<sub<2-y</sub<Se<sub<2</sub< with a critical temperature of 32 K，is made more difficult by the fact that it separates into two phases- a dominant antiferromagnetic insulating phase K<sub<2</sub<Fe<sub<4</sub<Se<sub<5</sub<，and a minority superconducting phase. In this paper，we identify a three-dimensional network of superconducting filaments within this material and present evidence to suggest that the superconducting phase consists of a single Fe vacancy of every eight Fe-sites arranged in a √8× √10 paral⁃lelogram structure.