Abstract
We have synthesized polycrystalline samples of Fe1.11(Te1−x S x ) and single crystals of Fe1+y (Te0.88S0.12), and characterized their properties. Our results show that the solid solution of S in the Fe1.11Te tetragonal lattice is limited, ∼10%. We observed superconductivity at ∼8 K in both polycrystalline samples and single crystals. Magnetization measurements reveal that the volume fraction is small for this superconducting phase in both polycrystalline samples as-synthesized and single crystals as-grown. It is found that annealing in air enhances the superconducting fraction; the maximum fraction is almost 100% in the single crystals annealed in air at 300°C. We discuss the effect of annealing on superconductivity and transport properties at the normal state in the Fe1+y (Te1−x S x ) system in terms of decrease of the excess Fe.
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