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

Abstract

WO${}_{3-x}$F${}_x$ ($x$ $\le$ 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${}_{3-x}$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 $\le$ $x$ $\le$ 0.45. This easy fluorination method may be applicable to other systems and presents an opportunity for finding new oxyfluoride superconductors.