Effects of Annealing under Tellurium Vapor for   Fe$_{1.03}$Te$_{0.8}$Se$_{0.2}$ Single Crystals
  In this study, the effects of annealing under tellurium vapor have been investigated for Fe$_{1.03}$Te$_{0.8}$Se$_{0.2}$ single crystals. The as-grown crystal is not superconducting. After annealing it at 400 $^\circ$C for 250 h in tellurium (Te) vapor, it shows metallic resistivity temperature dependence below 150 K and a sharp superconducting transition at 13 K. The sample also shows a full magnetic shielding effect at low temperatures. The improvement in superconductivity has been attributed to the removal of excess Fe, which is inevitably incorporated in the as-grown crystals, by the annealing. 
Yuta Koshika, Tomohiro Usui, Shintaro Adachi, Takao Watanabe, Kouhei   Sakano, Shalamujiang Simayi, and Masahito Yoshizawa
cond-mat.supr-con cond-mat.str-el