Structural and electronic response upon hole-doping of rare-earth iron   oxyarsenides Nd1-xSrxFeAsO (0 < x < 0.2)
  Hole-doping of NdFeAsO via partial replacement of Nd3+ by Sr2+ is a successful route to obtain superconducting phases (Tc = 13.5 K for a Sr2+ content of 20%); however, the structural and electronic response with doping is different from and non-symmetric to that in the electron-doped side of the phase diagram. 
Karolina Kasperkiewicz, Jan-Willem G. Bos, Andrew N. Fitch, Kosmas   Prassides, and Serena Margadonna