Synthesis, characterization and low temperature studies of iron chalcogenide superconductors

We have synthesized tetragonal iron selenide and telluride superconductors through solid state reaction at 450 °C and 550 °C, respectively. These synthesis temperatures have been established by optimization. Electrical resistivity and magnetic susceptibility measurements (4.2–300 K) confirm superconductivity with TC of around 8.5 K in all selenide samples of nominal composition Fe1+δSe (δ = 0.02–0.22). However, Scanning Electron Microscopy/Energy Dispersive Spectroscopy studies clearly indicate that the actual stoichiometric ratio of Fe:Se for all the samples synthesized is around 1:1. Also all the samples exhibit identical phase transition temperatures from tetragonal to orthorhombic structure below ∼100 K implying identical phase composition. The partial substitution of Se by Te leads to an enhancement of TC to ∼13 K. The non-superconducting telluride Fe1.09Te exhibits a metal–insulator phase transition at ∼82 K. Substitution studies of this telluride system by S and Si have in addition been carried out to investigate if chemical pressure induces superconductivity.