Effect of Water on the IR Properties of Mg 2+ Intercalated Electrochromic Nb 2 O 5 Thin Films
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0972-AA09-13
Effect of Water on the IR Properties of Mg2+ Intercalated Electrochromic Nb2O5 Thin Films Gargi Agarwal and G. B. Reddy Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016, India ABSTRACT Sol-gel derived Nb2O5 thin films were intercalated with Mg2+,using the nonaqueous solution of Mg(ClO4)2 in propylene carbonate (pc) as the electrolyte. 2% and 4% (volume %) water was added to the electrolyte to study the effect of water on the electrochromic properties of Nb2O5. This paper presents the changes in optical and structural properties of the intercalated films with and without water in the electrolyte. The ratio (x) of the Mg2+ and Nb atoms has been controlled by optimizing the intercalation duration under a constant current density. The reduction in transmittance (T) on intercalation (for x= 0.8) increased by 15% with 4% water in the electrolyte, compared to the film intercalated without water. FTIR studies show that water is incorporated in the films on intercalation and small quantities of Mg(OH)2 and Nb-OH are formed along with Mg-O-Nb bonds. The presence of water in electrolyte decreases water content in the films and enhances the formation of Mg(OH)2, Mg-O-Nb and Nb-OH bonds. The recovery of Mg2+ on deintercalation is slightly reduced in presence of water in the electrolyte. The cyclic stability of the films intercalated without water is more than that of the films intercalated in presence of water. Keywords: Electrochromic, Nb2O5, Intercalation, Sol-gel, Magnesium, Water. INTRODUCTION
Electrochromic materials enable dynamic control of throughput of radiant energy and play a significant role in energy-efficient ‘smart windows’ in order to reduce the cooling and lighting loads of buildings. Electrochromic behavior in many transition metal oxides like WO3, MoO3, and V2O5 has already been studied for the last few decades [1]. Nb2O5 has attracted extensive interest in the recent years as a promising cathodic electrochromic material [1]. Nb2O5 shows excellent chemical stability and corrosion resistance in both acidic and alkaline medium [2]. It shows a variety of colors on intercalation from brown for amorphous layer to grey for crystalline layers with small crystallite sizes (< 25 nm) and blue for crystalline layers with large crystallite sizes (>30 nm) [3]. Recently there has been an increased interest in using bivalent Mg2+ as intercalants for use in electrochromic windows for various reasons [4]. Pereira et al.[5] have reported successful intercalation of Mg2+ in V2O5. An in-depth study of Mg2+ intercalation in layered MoO3 and the effect of water vapor on the intercalation phenomenon has been reported by one of the authors [6-7]. The electrochromic behavior
of Nb2O5 thin films with Mg2+ has also been reported by the authors [8]. It has been shown that water plays an important role in the Li+ intercalation and coloration behavior of electrochromic materials thus deciding the performance of an electrochromic device [3]. However, no reports
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