Superconductivity in sol-gel prepared amorphous thin films of Na$_{x}$WO$_{3-y}$

Sol-gel prepared tungsten trioxide (WO$_{3-y})$ thin film (300 nm) electrochemically intercalated with sodium ions exhibits a pronounced diamagnetic and zero resistance onsets at 4.7 K. XRD spectrum of Na$_{x}$WO$_{3-y}$ film shows amorphous structure with very small peaks indicating to nucleation of hexagonal nanocrystals. Shift of $T_{c}$ at different applied currents and magnetic fields indicate on very high critical currents and critical magnetic fields. Despite of small resistivity onset starting at 6 K, the magnetic susceptibility measurements exhibit ZFC onset at 4.7 K, where the resistivity curve has second stronger temperature decline. This is a first observation of superconducting phase transition in amorphous tungsten bronzes.