%0 Journal Article %J Phase Transitions %D 2008 %T Phase transitions in non-hydride switchable mirror thin films %A Thomas J. Richardson %K electrochromism %K optoelectronics %K Switchable mirrors %K thin films %X

Switchable mirrors modulate incident light by changes in the reflectivity of thin films that are converted by chemical reactions from a metallic reflective state to a semiconducting transparent state. The reactions may be effected by exposure to a gas, by treatment with a liquid reagent, or by electrochemical means. The changes in optical properties coincide with phase transformations. In the examples reviewed here, the reactions are accompanied by substantial volume changes and atomic rearrangement. Bismuth, antimony, and antimony alloy films are switched by electrochemical lithiation. Copper films are electrochemically oxidized to Cu(I) and Cu(II) oxides, which are transparent and opaque, respectively. Morphological changes in all films during cycling lead to degradation in performance without loss of active material. Strategies to improve the cycling stability of these systems are discussed.

%B Phase Transitions %V 81 %P 807 - 813 %8 07/2008 %N 7-8 %! Phase Transitions %R 10.1080/01411590801911406 %0 Journal Article %J Solar Energy Materials and Solar Cells %D 1995 %T Optical and Electrochemical Characteristics of Niobium Oxide Films Prepared by Sol-Gel Process and Magnetron Sputtering: A Comparison %A Nilgün Özer %A Carl M Lampert %A Michael D. Rubin %K D.C. magnetron sputtering %K electrochromism %K Niobia %K optical properties %K sol-gel deposition %X

Electrochromic niobia (Nb205) coatings were prepared by the sot-gel spin-coating and d.c. magnetron sputtering techniques. Parameters were investigated for the process fabrication of sol-gel spin coated Nb205 films exhibiting high coloration efficiency comparable with that d.c. magnetron sputtered niobia films. X-ray diffraction studies (XRD) showed that the sot-gel deposited and magnetron sputtered films heat treated at temperatures below 450°C, were amorphous, whereas those heat treated at higher temperatures were slightly crystalline. X-ray photoelectron spectroscopy (XPS) studies showed that the stoichiometry of the films was Nb205. The refractive index and electrochromic coloration were found to depend on the preparation technique. Both films showed low absorption and high transparency in the visible range. We found that the n, k values of the sot-gel deposited films to be lower than for the sputtered films. The n and k values were n = 1.82 and k = 3 × 10−3, and n = 2.28 and k = 4 × 10−3 at 530 urn for sot-gel deposited and sputtered films, respectively. The electrochemical behavior and structural changes were investigated in 1 M LiC104/propylene carbonate solution. Using the electrochemical measurements and X-ray photoelectron spectroscopy, the probable electrode reaction with the lithiation and delithiation is Nb2O5 + x Li+ + x e ↔ LixNb205. Cyclic voltametric (CV) measurements showed that both Nb205 films exhibits electrochemical reversibility beyond 1200 cycles without change in performance. “In situ” optical measurement revealed that those films exhibit an electrochromic effect in the spectral range 300 < λ < 2100 nm but remain unchanged in the infrared spectral range. The change in visible transmittance was 40% for 250 nm thick electrodes. Spectroelectrochemical measurements showed that spin coated films were essentially electrochemically equivalent to those prepared by d.c. magnetron sputter deposition.

%B Solar Energy Materials and Solar Cells %V 40 %P 285-296 %8 08/1996 %G eng %N 4 %1

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%2 LBNL-39007 %& 285 %R 10.1016/0927-0248(95)00147-6