Cation intercalation in sputter-deposited W oxide films

Intercalation of Li, Na, and K ions into sputtered amorphous and monoclinic W oxide has been studied electrochemically and by x-ray diffraction. It was found that both Li and K intercalation, at low concentrations, caused a phase separation in the crystalline W oxide, while Na intercalation, at low concentrations, accurately followed the lattice-gas model [A. J. Berlinsky, W. G. Unruh, W. R. McKinnon, and R. R. Haering, Solid State Commun. 31, 135 (1979)]. The lattice-gas model was also used to extract information about the electrochemical response at high concentrations of all three types of intercalants. At low concentrations the net interaction between the intercalated ions was found to be attractive, while at higher concentrations the interaction was repulsive. Intercalation of alkali ions into amorphous W oxide could be modeled with a Gaussian distribution of site energies. The distribution of Li ions was found to be narrower and peaked at a lower energy than that of Na and K ions.