Structural Phase Separation in K0.8Fe1.6+xSe2 Superconductors

Abstract

Structural investigations on the K0.8Fe1.6+xSe2 superconducting materials have revealed microstripes arising from phase separation. Two coexisting structural phases can be characterized by modulations of q1 = 1/5[3a* + b*], the antiferromagnetic phase K0.8Fe1.6Se2, and q2 = 1/2[a* + b*], the superconducting phase KyFe2Se2, respectively. These stripe patterns also show visible correlation with the anisotropic assembly of superconducting particles along the [110] and [11̅0] directions. In addition to the notable stripe structures, a nanoscale phase separation also appears in the present superconducting system as clearly observed by high-resolution transmission electron microscopy. Certain nanoscale structural features in this heterogeneous system can be qualitatively understood by the percolation scenario.