Tellurium substitution effect on superconductivity of the alpha-phase   Iron Selenide
  We have carried out a systematic study of the PbO-type compound FeSe_{1-x}Te_x (x = 0~1), where Te substitution effect on superconductivity is investigated. It is found that superconducting transition temperature reaches a maximum of Tc=15.2K at about 50% Te substitution. The pressure-enhanced Tc of FeSe0.5Te0.5 is more than 10 times larger than that of FeSe. Interestingly, FeTe is no longer superconducting. A low temperature structural distortion changes FeTe from triclinic symmetry to orthorhombic symmetry. We believe that this structural change breaks the magnetic symmetry and suppresses superconductivity in FeTe. 
Kuo-Wei Yeh, Tzu-Wen Huang, Yi-Lin Huang, Ta-Kun Chen, Fong-Chi Hsu,   Phillip M. Wu, Yong-Chi Lee, Yan-Yi Chu, Chi-Liang Ch...