Novel Iridium-Doped Superconductor

Replacing some of the iron atoms with iridium in rare-earth iron arsenides leads to a new type of superconducting compound, according to scientists in China and Australia who prepared the material (J. Am. Chem. Soc., DOI: 10.1021/ja901065p). Yong Zhao and Yong Liang Chen of Southwest Jiaotong University and coworkers report that the critical transition temperature (T_c) of iridium-doped SmFeAsO increases with iridium concentration, reaching a maximum of 16 K at an iridium-doping level of 15% (SmFe_0.85Ir_0.15AsO). Iron arsenides with T_c values as high as 56 K have been reported, but the new compound is unique in terms of its transition-metal composition—until now, only cobalt, and to a lesser extent nickel, has been able to induce superconductivity in iron-arsenide-based compounds. Following last year’s discovery of high-temperature iron-arsenide superconductors, researchers around the globe were quick to synthesize numerous related compounds in an effort to boost the T_c (C&EN, Oct. 20, 2008, page 15). Most compounds were made by replacing some oxygen with fluorine or one rare-earth element for another. The latest results highlight an alternative route in the search for new superconductors with enhanced properties, the team says.