Electronic Transport in AmorphousHxWO3

We report measurements of the electrical conductivity, $\sigma$, of thin amorphous films of hydrogen tungsten bronze, ${\mathrm{H}}_x\mathrm{W}{\mathrm{O}}_3$, as a function of temperature and hydrogen/tungsten ratio, $x$. For $x\lesssim 0.3$ the temperature dependence of $\sigma$ can be explained by the variable-range hopping model. At $x=0.32\mathrm{}$ an insulator-to-metal transition occurs with a minimum metallic conductance of about 5.1 × ${10}^{-5\mathrm{}}$ ${\mathrm{\Omega }}^{-1\mathrm{}}$.