Variations in the structural, optical and electrochemical properties of CeO 2 –TiO 2 films as a function of TiO 2 content Amita Verma a , Amish G. Joshi a , A.K. Bakhshi b , S.M. Shivaprasad a , S.A. Agnihotry a, * a National Physical Laboratory, New Delhi 110012, India b Department of Chemistry, University of Delhi, Delhi 110007, India Received 25 May 2005; received in revised form 4 July 2005; accepted 28 July 2005 Available online 15 September 2005 Abstract Alcohol based sols of cerium chloride (CeCl 3 7H 2 O) and titanium propoxide (Ti(OPr) 4 ) in ethanol mixed in different mole ratios have yielded mixed oxide films on densification at 500 8C. The reversibility of the intercalation/deintercalation reactions has shown electrochemical stability of the films. Addition of TiO 2 in an equivalent mole ratio manifests in producing highly transparent films with appreciable ion storage capacity. The electrochemical studies have revealed the significant role of TiO 2 in controlling the ion storage capacity of the films, as it tends to induce the disorder. In addition, the films prepared from an aged sol are observed to exhibit a much higher ion storage capacity than the films deposited using the as-prepared sol. The X-ray photoelectron spectroscopic studies have provided information on the variation of Ce 4+ /Ce 3+ ratio as a function of increased TiO 2 content in the films. This study has led to a better understanding of the increased ion storage capacity with the increased TiO 2 proportion. The transmission electron microscopic study has demonstrated the presence of CeO 2 nanograins even in films, which are amorphous to X-rays. Elucidation of the structural, optical and electrochemical features of the films has yielded information on aspects relevant to their usage in transmissive electrochromic devices. The films have been found to exhibit properties that can find application as counter electrode in electrochromic smart windows in which they are able to retain their transparency under charge insertion, high enough for practical uses. Also, the fastest coloration–bleaching kinetics for the primary electrochromic electrode (WO 3 ) working in combination with Ce/Ti (1:1) electrode stimulates the use of latter in electrochromic windows (ECWs). # 2005 Elsevier B.V. All rights reserved. PACS: 68.55.a; 73.61.Tm; 81.20.Fw Keywords: Sol–gel; Spin coating; CeO 2 –TiO 2 ; Passive counter electrode; Electrochromism www.elsevier.com/locate/apsusc Applied Surface Science 252 (2006) 5131–5142 * Corresponding author. Tel.: +91 11 25742610/2283; fax: +91 11 25726938. E-mail address: agni@mail.nplindia.ernet.in (S.A. Agnihotry). 0169-4332/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2005.07.035