Superconductivity and transport properties in Th and F codoped Sm1-xThxFeAsO1-yFy
A series of Th and F co-doped superconductors Sm1–xThxFeAsO1–yFy are synthesized and the variation of superconductivity with the doping level is investigated. At the fixed Th doping level x = 0.1, the superconducting transition temperature Tc increases monotonically with F content, and finally Tc reaches a maximum of about 55K around y = 0.1, and saturates for even more F content (y = 0.15). Similar to the SmFeAsO1–yFy system, the normal state thermopower increases monotonically with the doping level. However the decrease of Tc in the 'overdoped' regime is not observed and possible explanation is discussed.