Chemical control of interstitial iron leading to superconductivity in Fe 1+xTe 0.7Se 0.3

Although it possesses the simple layered topology of the tetragonal anti-PO structure, the Fe(Te,Se) series has a complex structural and magnetic phase diagram that is dependent on composition and occupancy of a secondary interstitial Fe site. Here we show that superconductivity in Fe 1+xTe 0.7Se 0.3 is enhanced by topotactic deintercalation of the interstitial iron with iodine, demonstrating the competing roles of the two iron positions. We follow the evolution of the structure and magnetic properties as a function of interstitial iron. Powder neutron diffraction reveals a flattening of the Fe(Te,Se) 4 tetrahedron on Fe removal and an unusual temperature dependence of the lattice parameters that increases strongly below 150 K along with lattice strain. Inelastic neutron scattering shows gapless paramagnetic scattering evolves into a gapped excitation at 6 meV on removal of interstitial iron. This work highlights the robustness of the superconductivity across different Fe(Te,Se) compositions and geometries. © The Royal Society of Chemistry 2011.