Doped WO3 thin film is a nano-composite electrochromic film, which may be used to building glass for energy-saving. Wherein, an organic-inorganic multi-doped tungstic acid sol is prepared by a sol-gel technique. But why must the sol be doped?
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Experts have found that the pure tungstic acid sol system produced by ion exchange is extremely unstable, and the tungstic acid turns into a yellow-green gel within twenty minutes. The [WO4]^2-ion produced after passing through the column forms a paratungstate ion [HW6O21]^5- and a polymerized paratungstic acid A ion [(HW6O20)n]^3n-. Under strong acidic conditions, the paratungstic acid A ion [(HW6O20)n]^3n- is continuously converted into unstable paratungstic acid H3[H3W6O21], and tungstic acid-based hydrated tungsten oxide H2WO4?nH2O, and the sol is coagulated. Therefore, such an unstable sol is not suitable for the precursor spin coating of electrochromic materials, and must be doped to enhance the stability of the sol.
