Unstructured electrochromic mirrors with variable reflectance have been developed on the basis of hydrogen tungsten bronzes. The characteristic compounds of these devices are (1) solid ion-conducting layers ("electrolytes") resulting in only few micrometer thick all-solid-state systems, which can be enclosed between the substrate and a second glass plate and are thus protected from the environment, (2) integrated reflecting metal layers, and (3) hydrogen-storing electrochromic layers. Two basically different constructions are feasible. In "diffusion-driven" devices the bronze is formed (decomposed) by the chemical reaction x/2 H2+ W03⇔HxW03, in "field-driven" systems an electrochemical bronze formation (decomposition), x H + W03+ x e HxW03, takes place. The modes of construction are presented and compared, the electrochemistry of the thin layer cells involved is discussed, the prop-erties of devices according to the state of development are reported, and possible applications, e.g. as glare-free, inside and outside, automotive rear view mirrors with adjustable reflectance, are briefly described.
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