Alternating current impedance and Raman spectroscopic study on electrochromic a-WO3 films

The chemical diffusion of lithium ions in a-LixWO3 films is investigated us ing alternating current impedance spectroscopy and Raman scattering measure ments. The diffusion coefficients increase with increasing x in a-LixWO3 up to x=0.072 and then decrease. Raman measurements show that the W6+=O/O-W6-O ratio also increases at the early stage of lithium insertion and then de creases with further lithium insertion. We conclude that the diffusion kine tics of lithium ions in a-LixWO3 films is very closely related to the W6+=O /O-W6+-O ratio. (C) 2000 American Institute of Physics. [S0003-6951(00)0462 6-X].