Raman study of thermochromic phase transition in tungsten trioxide nanowires

Tungsten trioxide $(WO3)$ nanowires were synthesized by thermal evaporation of tungsten powder in two steps: tungsten suboxide $(WO3−x)$ nanowires were synthesized, and then oxidized in $O2$ ambient and transformed into $WO3$ nanowires. Raman spectroscopy was applied to study the thermochromic phase transition of one-dimensional $WO3$ nanowires. From the temperature dependence of the characteristic mode at $33cm−1$ in $WO3$⁠, the phase transition temperature was determined. It was found that the phase transition of $WO3$ nanowires was reversible and the phase transition temperatures were even lower than that of $WO3$ nanopowder.