Sputter deposited cerium–vanadium oxide: optical characterization and electrochromic behavior

Abstract

Vanadium pentoxide has been the subject of many works owing to its capacity to host large amounts of lithium. Many studies where V 2O 5 has been mixed with different transparent oxides, such as CeO 2, ZrO 2, TiO 2, have been performed in order to preserve the ion-storage capacity and compensate the unwanted multicolor cathodic electrochromism. In the present work, we report on the optical properties of cerium and vanadium mixed oxides obtained by radio frequency sputtering in reactive Ar+O 2 atmosphere. Since the electrochromic properties of thin films strongly depend on the oxidation state of the transition metal in the oxide, the role of oxygen partial pressure during the deposition is of fundamental importance. A set of samples was deposited by decreasing the oxygen partial pressure in the chamber from 1/6 to 1/1000 of the total pressure and their optical properties were compared to those of the samples deposited in pure argon. The majority of deposited films changes coloration from yellowish to transparent upon lithium insertion, showing an anodic-like electrochromic behavior. Optical constants (refractive index and extinction coefficient) and film thickness were evaluated in the visible range from photometric measurements of both as-deposited and intercalated films.