Superconductivity was achieved in PrFeAsO by partially substituting ${\text{Pr}}^{3+}$ with ${\text{Sr}}^{2+}$. The electrical transport properties and structure of this superconductor ${\text{Pr}}_{1-x}{\text{Sr}}_x\text{FeAsO}$ at different doping levels $\left(x=0.05\sim 0.25\right)$ were investigated systematically. It was found that the lattice constants ($a$ and $c$ axes) increase monotonously with Sr or hole concentration. The superconducting transition temperature at about 16.3 K (95% ${\rho }_n$) was observed around the doping level of $0.20\sim 0.25$. A detailed investigation was carried out in the sample with doping level of $x=0.25$. The domination of holelike charge carriers in this material was confirmed by Hall-effect measurements. The magnetoresistance (MR) behavior can be well described by a simple two-band model. The upper critical field of the sample with $T_c=16.3\text{K}$ $\left(x=0.25\right)$ was estimated to be beyond 45 T. Our results suggest that the hole-doped samples may have higher upper critical fields comparing to the electron-doped ones, due to the higher quasiparticle density of states at the Fermi level.

• Received 9 October 2008

DOI:https://doi.org/10.1103/PhysRevB.79.104501