Showing papers by "Claes-Göran Granqvist published in 1997"

Angular selective window coatings: theory and experiments

Abstract: This review is devoted to the angular selectivity that can be obtained in thin films prepared under conditions such that they contain inclined absorbing regions of sizes much smaller than the wavelength of visible light. The films are of considerable interest as window coatings for energy-conscious architecture and, potentially, in the automotive sector. The theoretical basis for modelling the optical properties is presented, comprising rigorous bounds on the dielectric function, effective medium theories pertinent to different microgeometries and equations for treating the optics of anisotropic thin films. Experimental data are reported for films made by oblique-angle evaporation of Cr and for reactive and non-reactive oblique-angle sputtering of Cr, Al, Ti and W. The highest angular selectivity was obtained with evaporated Cr, whereas the highest luminous transmittance, combined with some angular selectivity, was found with reactively sputtered Al. Films made from Ti showed angular selectivity mainly in the infrared, whereas films made from W could display angular selective electrochromism. Samples of several types were subjected to elaborate theoretical analysis using effective-medium theories and it was seen that theory and experiment could be reconciled using plausible parameters to specify the microstructures of the films. Thus it appears that the angular, spectral and polarization dependences of obliquely deposited films can be understood, at least approximately, in terms of conceptually simple theoretical models.

Towards the smart window: progress in electrochromics

Abstract: Electrochromic devices have the ability to produce reversible and persistent changes of their optical properties. The phenomenon is associated with joint ion and electron transport into/out of an electrochromic thin film, in most cases being a transition metal oxide. This paper outlines the various applications of such devices in smart windows suitable for energy-conscious architecture, in variable-reflectance mirrors, and in display devices. Critical materials issues and design concepts are discussed. The paper also covers two specific research topics: computed electronic structure of crystalline WO3 incorporating ionic species, showing how reflectance modulation emerges from a first-principles calculation; and Li+ dynamics in heavily disordered Ti oxide, illustrating how diffusion constants derived from impedance spectroscopy can be reconciled with the Anderson—Stuart model.

Transparent ion intercalation films of Zr–Ce oxide

Abstract: Zr–Ce oxide films were made by reactive dc magnetron cosputtering. The elemental composition was determined by Rutherford backscattering spectrometery and the crystalline structure by x-ray diffraction. Li intercalation/deintercalation was accomplished potentiodynamically in a liquid electrolyte. The films remained fully transparent irrespective of their degree of lithiation, which may be reconciled with a population/depopulation of Ce 4f levels.

Li intercalation in transparent Ti-Ce oxide films: Energetics and ion dynamics

Abstract: Films of Ti dioxide, mixed Ti–Ce oxide, and Ce dioxide were produced by reactive dc magnetron sputtering. Electrochemical lithiation was probed by chronopotentiometry, cyclic voltammetry together with optical transmittance recording, and impedance spectroscopy. Evidence was found for inserted electrons being accommodated in Ce 4f states; this contention was supported by preliminary results from x-ray absorption fine-structure spectroscopy. These electrons do not produce luminous electrochromism. The variation of the chemical diffusion coefficient of Li, with film composition and Li content, was also studied.

Electrochromic control of thin film light scattering

Abstract: Total and diffuse reflectance spectra were measured on Al surfaces covered with electrochromic W oxide films in colored and bleached states. Vector perturbation theory was used for analyzing the spectra. The diffuse reflectance appeared to originate from correlated (uncorrelated) interface roughness when the W oxide film was fully colored (bleached). Assuming partially correlated interfaces led to agreement between experimental and calculated spectra. The use of an electrochromic film appears a promising method to control the relative contributions of the interfaces to the resulting scattering.

Aluminium oxide — Poly(vinyl acetate) composite electrolyte for electrochromic devices

Abstract: This report describes composite proton electrolytes composed of nanosize activated aluminium oxide particles with different surface acidity suspended in a poly(vinyl acetate)/glycerine matrix The conductivity of the composite was found to increase by going from basic to neutral to acidic aluminium oxide Tests in laminated electrochromic devices with tungsten oxide and nickel hydroxide films showed that the acidic electrolyte is compatible with WO3, the basic electrolyte is compatible with Ni(OH)2, and the neutral electrolyte is compatible with both of the electrodes