The so-called plastic technology first developed for Li-ion batteries is demonstrated for its potential optical applications in infrared emissivity control. WO 3 ‚H 2 O powder embedded in a plastic matrix is used as the active component in the LiCoO 2 /Li electrolyte/WO 3 ‚H 2 O system. The role of the microstructure of WO 3 ‚H 2 O as an electrochromic material is investigated. For instance, platelet-shaped grains with a surface area as large as 15 µm 2 induce a large improvement in device contrast properties. Reflectance measurements show a 53% contrast between the bleached and colored states over the 8-12 µm range. This effect is likely rooted in the free electron mobility in addition to scattering and phonon effects. The optical modulation performance over the range 2.5-20 µm compares favorably with literature results on solid devices built from annealed and sputtered m-WO 3 thin films.

The interest in studying the electrical properties of WO(3) x H(2)O powders is made absolutely necessary because their infrared modulation properties depend on their morphologies and electronic populations. Broadband dielectric and resistivity spectra of WO(3) x H(2)O powders were recorded in a frequency range of 10(3)-10(10) Hz at temperatures varying between 200 and 300 K. Complex resistivity and permittivity diagrams have permitted thermal behavior of both dc-conductivity and permittivity to be obtained. A dielectric relaxation is found, attributed to water molecules motions. The role of the powder morphology has been investigated on two types of compounds: the first one being constituted by nanometric particles and the second by micrometric particles. Strong differences are observed in the thermal behaviors of the dc-conductivities (activation energies). Particle size effect is evidenced, giving rise to stronger electron localization on the nanometric particles. The permittivity values and the dynamical behavior of the structural water are also influenced by the particle size effect. A strong interaction between moving polarons and water molecules has been determined.