Formation of nano-rod sodium tungstate film by sodium ion diffusion

摘要

Tungsten oxide (WO_3) and nano-rod sodium tungstate (Na_2W_2O_7) thin film was prepared by dip coating on slide glass (SG) and tin-doped indium oxide (ITO) coated glass in peroxotungstic acid (PTA) solution. Thermal analysis results showed that PTA is decomposed to tungsten oxide via multiple steps of WO_3·2/3H_2O, WO_3·1/3H_2O and WO_3. Monoclinic phase appeared on ITO glass at 400 ℃ and crystal growth occurred at 500 ℃. However, quite different crystallization behavior appeared on SG due to sodium ion diffusion. At 400 ℃, rectangular shape crystals identified as Na_2W_4O_(13) appeared in amorphous matrix, and grew to bundles of rod-shaped Na_2W_2O_7 and Na2W_4O_(13) phase at 500 ℃. Raman scattering spectroscopy data confirmed the formation of Na_2W_4O_(13) and Na_2W_2O_7 at 500℃. The understanding of crystallization behavior and sodium ion diffusion into WO_3 thin film on different substrates may be helpful to the application area of electrochromic windows or photocatalyst.