Sputter-deposited cerium vanadium mixed oxide as counter- electrode for electrochromic devices E. Masetti a, *, F. Varsano b , F. Decker b a ENEA, Casaccia Thin Film Optics Lab., Via Anguillarese 301, 00060 Rome, Italy b Chemistry Department, Universita' di Roma `La Sapienza', P.le A. Moro 5, 00185 Rome, Italy Received 7 September 1998; received in revised form 23 November 1998 Abstract Oxide ®lms deposited by reactive radio frequency sputtering of target made of mixed CeO 2 and V 2 O 5 (1:1) powders show an anodic electrochromic character upon lithium insertion. As-deposited ®lms look yellowish and become fully transparent for an inserted charge of 30 mC/cm 2 of Li ions. A total charge of 60 mC/cm 2 has been reversible cycled in the 1 to 5 V versus Li range in an electrochemical cell without any signi®cant degradation. Following these preliminary results, ®lms of Ce±V mixed oxide made by r.f. sputtering are suitable for working in tandem with tungsten oxide in a practical electrochromic device. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Electrochromic materials; Ce±V oxide; Mixed oxide; r.f. sputtering; Thin ®lms Vanadium oxide (V 2 O 5 ) is known to be a very good intercalation material whose main drawback, when used as counter-electrode in an electrochromic device, is its residual coloration in the reduced state [1]. The idea behind this study is to improve its optical proper- ties without losing the charge capacity, suitable for working in tandem with tungsten oxide. CeO 2 has been studied in the last years for its use as a passive counter-electrode because it retains its high transparency in both the oxidised and the reduced state [2]. Moreover, it provides an ecient UV shield related to its strong absorption for wavelengths below 380 nm. Nevertheless, its reaction kinetics are slow and its charge capacity is not satisfactory for practical elec- trochromic applications. Several attempts have been made in order to improve its electrochemical properties by way of mixing the oxide with other materials such as Sn, Ti and Zr oxides [3,4]. Recently, it was thought that the addition of CeO 2 to V 2 O 5 might quench vanadium oxide's undesired re- sidual coloration in the bleached state. In fact, cerium± vanadium mixed oxides made using the sol±gel route have proved to be interesting for their use as counter- electrode in electrochromic windows [5]. In this work we present the optical and electroche- mical behaviour of thin ®lms of mixed cerium and va- nadium oxide obtained by r.f. sputtering in a reactive atmosphere of argon and oxygen. To our best knowl- edge, this is the ®rst time that electrochromic Ce±V mixed oxide has been prepared by a vacuum technique. Even if the experimental results we report here are very preliminary and a more systematic study is still in progress, we consider them as interesting for a short communication. Usually, ®lms of mixed oxides are deposited by the sputtering technique using the so-called `co-sputtering' method where targets of dierent materials are sput- Electrochimica Acta 44 (1999) 3117±3119 0013-4686/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0013-4686(99)00028-6 * Corresponding author. Fax: +39-6-3048-6364. E-mail address: masetti@casaccia.enea.it (E. Masetti)