Effects of composition and structure on gasochromic coloration of tungsten oxide films investigated with XRD and RBS

The effects of composition and structure on gasochromic coloration of tungsten oxide films for hydrogen have been investigated. Tungsten oxide films with various O/W atomic ratios from 1.5 to 3.0 are prepared using a reactive rf magnetron sputtering from a tungsten target at different oxygen partial pressures. The films were deposited on quartz and carbon substrates at 200 °C. The O/W atomic ratio and crystallographic structure of the films were determined by Rutherford backscattering spectroscopy and X-ray diffraction. The gasochromic properties of the films were examined by use of optical transmittance in exposure in 1% H2/Ar atmosphere. The stoichiometric WO3 film with amorphous structure resulted in superior gasochromic coloration. The decrease in gasochromic performance was caused by non-stoichiometric WO3 films with amorphous structure or stoichiometric WO3 films crystallized with post-annealing at temperatures higher than 300 °C in air. It suggests that the gasochromic coloration of tungsten oxide films for hydrogen is strongly influenced by the composition and structure.