Superconductivity and Phase Diagram in the Iron-based Arsenic-oxides   ReFeAsO1-delta (Re = rare earth metal) without F-Doping
  Here we report a new class of superconductors prepared by high pressure synthesis in the quaternary family ReFeAsO1-delta (Re = Sm, Nd, Pr, Ce, La) without fluorine doping. The onset superconducting critical temperature (Tc) in these compounds increases with the reduction of Re atom size, and the highest Tc obtained so far is 55 K in SmFeAsO1-delta. For the NdFeAsO1-delta system with different oxygen concentration a dome-shaped phase diagram was found. 
Zhi-An Ren, Guang-Can Che, Xiao-Li Dong, Jie Yang, Wei Lu, Wei Yi,   Xiao-Li Shen, Zheng-Cai Li, Li-Ling Sun, Fang Zhou, Zho...