Enhancement of superconductivity by Sb-doping in the hole-doped iron-pnictide superconductor Pr sub(1-x)Sr sub(x)FeAsO

The search for new high transition temperature (T sub(c)) superconductivity is one of the most challenging tasks both on the condensed matter physics and material science. Here we report that the onset T sub(c) of Sr-doped PrFeAsO is enhanced to 22 K by Sb-doping on the As-site. Moreover, the behavior of resistance in the normal states shows a systematic evolution with the increase of Sb contents, indicating the change of scattering conditions induced by Sb doping. The lattice constants remain almost unchanged when the Sb concentration goes up. In contrast, P-doping is found to be detrimental to superconductivity and to shrink the crystal lattice in the same system. Hall effect are also measured to investigate the conduction properties of the present Sr and Pn (Pn = Sb, P) co-doped system.