Phase separation and superconductivity in Fe 1+xTe 0.5Se 0.5

Fe 1+xTe 0.5Se 0.5 is the archetypical iron-based superconductor. Here we show that the superconducting state is controlled by the stacking of its anti-PbO layers, such that homogeneous ordering hinders superconductivity and the highest volume fractions are observed in phase separated structures as evidenced by either a distribution of lattice parameters or microstrain. © 2011 The Royal Society of Chemistry