Superconductivity in WO2.6F0.4 synthesized by reaction of WO3 with teflon

WO3-xFx (x <= 0.45) perovskite-like oxyfluorides were prepared by a chemically reducing fluorination route using the polymer polytetrafluoroethylene (teflon). The symmetry of the crystal structures of WO3-xFx changes from monoclinic to tetragonal to cubic as the fluorine content increases. Fluorine doping changes insulating WO3 to a metallic conductor, and superconductivity (T-c = 0.4 K) was discovered in the samples with fluorine contents of 0.41 <= x <= 0.45. This easy fluorination method may be applicable to other systems and presents an opportunity for finding new oxyfluoride superconductors.