The synthesis, structural characterization and superconductivity of FeSex with 0.80≤ x≤1.20

We have performed a detailed study on the synthesis, the characterization of structural phases and superconductivity of the binary FeSex system from the Fe-rich phase into the Se-rich phase with 0.80≤ x ≤1.20. The results indicate that by long-time lowtemperature annealing, single phase sample could be obtained near the composition of FeSe0.95 with the tetragonal PbO-type structure, while impurities of Fe or Fe7Se8 would appear if Fe enriched or Se enriched in the starting composition respectively. Bulk superconductivity was found to exist in highly Se deficient phase, but not the single phase, and superconductivity is very sensitive to the Se vacancy content. The anomalous downturn of resistivity around 100 K was eliminated in Se-rich phase, along with the suppression of the main superconducting phase. PACS: 74.70.-b, 74.70.Ad, 74.62.Bf