Electronic phase diagram of NdFe_1-x Rh_xAsO

We report on the electrical resistivity, thermoelectric power, and electronic phase diagram of rhodium-doped NdFeAsO. Rhodium doping suppresses the structural phase transition and spin-density wave observed in the undoped material, and superconductivity emerges at x close to 0.05, despite the distortion of FeAs₄ tetrahedra induced by the large size difference between Rh and Fe elements. The T_c (x) curve is domelike, and the highest T_c is reached at x=0.1, with T_c^onset =18K. An upturn of the electrical resistivity above T_c has been observed, with a Kondo-type behavior above T_c and a Fermi-liquid behavior close to room temperature.