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ABSTRACT Antimony-doped tin oxide (ATO) nanophase materials containing up to 43 mole% antimony have been synthesized by a wet-chemistry method. These ATO materials exhibit enhanced electrochromic properties for display devices. The performance of the display devices is related to the nanostructure of the synthesized ATO materials. The average sizes of the ATO nanocrystallites depend on dopant level, annealing conditions, and synthesis processes. Antimony inhibits the growth of tin dioxide nanocrystallites during annealing at moderate temperatures. At higher annealing temperatures, however, antimony segregates to form separate oxide phases and ATO nanocrystallites grow significantly. A systematic study of the structural evolution of the synthesized ATO materials is presented and the relationship between the nanostructure of the ATO materials and the enhanced performance of the corresponding electrochromic devices is discussed. INTRODUCTION Electrochromic devices, such as smart windows or displays, are able to change their optical properties reversibly under the action of an applied voltage pulse and the optical modulation is related to the capacity of the electrochromic material for charge injection and expulsion. While many types of chemical species exhibit electrochromism, only those with favorable electrochromic parameters are potentially useful in commercial applications [1]. Most applications require electrochromic materials with a high contrast ratio, coloration efficiency, cycle life, and write-erase efficiency. Among many potential electrochromic materials, metal oxides have been extensively investigated [1, 2]. These oxides have unique microstructures comprising octahedral building blocks of MeO 6 type that are connected by comer-sharing and/or edge-sharing configurations [2]. Antimony-doped tin oxide (ATO) materials have many interesting and useful properties for industrial applications: ATO materials have been used as oxidation catalysts, antistatic pigments, and components for fuel cells and gas sensors. ATO and indium-doped tin oxide (ITO) have been studied in order to measure both their inherent electrochromic properties and their capacity for charge storage [3]. Only very weak electrochromism was observed in ATO films [3]. We recently synthesized nanophase ATO materials that exhibited a surprisingly high level of electrochromism [4]. Although the electro-optical and the structural properties of ATO materials with low levels of Sb-dopant have been extensively investigated [5-7], the fundamental structural/chemical properties of heavily doped ATO materials have not been well understood. We report here some preliminary results of a systematic study of the structural evolution of tin oxide 47 Mat. Res. Soc. Symp. Proc. Vol. 501 ©1998 Materials Research Society

nanoparticles heavily doped with antimony, and correlate the nanostructure of the synthesized ATO materials to their electrochromic performance. EXPERIMENTAL METHODS The preparation of ATO powders, along with electrochemical and optical characteri