Superconductivity in Sr and Co co-doped PrFeAsO Original Research Article

Polycrystalline Sr and Co co-doped superconducting oxypnictides Pr1−ySryFe1−xCoxAsO were synthesized by solid state reaction method, and superconductivity was investigated by measuring resistivity, magnetic susceptibility and thermopower. In the PrFe1−xCoxAsO samples with only Co doping, Tc reaches a maximum of 16 K at x=0.075–0.1, and the variation of Tc with Co content (x) is dome-shaped, consistent with the other Co-doped 1 1 1 1 phase systems such as LaFe1−xCoxAsO and SmFe1−xCoxAsO. In the Co and Sr co-doped Pr0.8Sr0.2Fe1−xCoxAsO system, Tc reaches a maximum of about 16 K at x=0.15, and the Tc‐x dome shifts to higher Co content in the phase diagram of Tc versus Co content (x). Our result indicates that Sr doping effectively induces hole-type charge carriers in the PrFeAsO system and the disorder caused by Sr and Co dopants has little effect on Tc. The thermopower data confirms that Sr dopant is hole-type and Co dopant is electron-type. The shift of Tc‐x dome to higher Co content caused by Sr doping implies that the Sr dopant can compensate for the Co doping effect. The results suggest that there could be a universal dependence of Tc on charge carrier density in both hole-type and electron-type oxypnictide superconductors.