Electrochromic vanadium–pentoxide–based films: Structural, electrochemical, and optical properties

Crystalline VO2.5 films were prepared by reactive dc magnetron sputtering followed by annealing posttreatment. Lithium was inserted electrochemically from an electrolyte so that LixVO2.5 (0electromotive force (EMF) was recorded during Li intercalation. For lithiated samples, structure by x‐ray diffraction, optical properties by spectrophotometry in the 0.3–2.5 μm range, infrared reflectance by spectrophotometry in the 400–1200 cm−1 interval, and the mechanical stress by beam deflectometry were studied. Changes in lattice parameters, phonon spectra, and stress levels gave a consistent picture of the structural evolution. Measurements of optical absorption and EMF were interpreted within a conceptual model of interband transitions between the O 2p band and a split V 3d band. Durability and reversibility of the Li intercalation/deintercalation were verified by potentiodynamic measurements. For comparison, the properties of highly disordered films were also measured.