Superconductivity in WO2.6F0.4synthesized by reaction of WO3with teflon

WO${}_{3\ensuremath{-}x}$F${}_{x}$ ($x$ $\ensuremath{\le}$ 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 WO${}_{3\ensuremath{-}x}$F${}_{x}$ changes from monoclinic to tetragonal to cubic as the fluorine content increases. Fluorine doping changes insulating WO${}_{3}$ to a metallic conductor, and superconductivity (${T}_{c}$ $=$ 0.4 K) was discovered in the samples with fluorine contents of 0.41 $\ensuremath{\le}$ $x$ $\ensuremath{\le}$ 0.45. This easy fluorination method may be applicable to other systems and presents an opportunity for finding new oxyfluoride superconductors.