Substitution Effects on FeSe Superconductor

We have investigated the effect of atomic substitutions in the FeSe system, which exhibits the simplest crystal structure among the iron-based Superconductors. An enhancement of the superconducting transition temperature T-c was observed with the substitution of S or Te for Se; the T-c increased with S substitution by up to 20%, and also increased with Te Substitution up to 75%. In contrast, Co or Ni substitutions for the Fe site significantly suppressed superconductivity. In this work we present a detailed description of the substitution technique employed to determine T-c in the FeSe system.