D. Dini et al., Stress changes in electrochromic thin film electrodes: Laser beam deflection method (LBDM) as a tool for the analysis of intercalation processes, SOL EN MAT, 56(3-4), 1999, pp. 213-221
The mechanical effects of the intercalation processes in electrochromic WO3
thin films are reported here and discussed. In particular the electrochemi
cal insertion of H, Li and Na ions in WO3 was studied by means of laser bea
m deflection method (LBDM). Linear changes of WO3 stress were observed for
small amounts of the inserted charge and linearity was always associated wi
th a reversible mechanical behavior of thin films. An explanation in terms
of homogeneity of the insertion is given. An analogous trend was also verif
ied in the absorbance vs. charge curves. As a consequence the constancy of
the electrochromic efficiency values for the three different ions was found
. In this way it was possible to determine a full reversible behavior for M
xWO3 in the composition range O less than or equal to x less than or equal
to 0.2. The onset of new phases formation when x exceeded previous upper li
mit, was observed during Li and Na intercalation. Such transitions brought
about the loss of optical and mechanical reversibility. During prolonged hy
drogen insertion a reversible slope inversion occurred in stress curve so t
hat it was necessary to take into account different possible mechanisms of
the WO3 electrochromic reaction. (C) 1999 Elsevier Science B.V. All rights
reserved.