Evolution from vanadium pentoxide xerogel to sodium-containing vanadates in thin films on ITO-coated glasses

In this work, the mechanism of the 'gelation' process and the thermal-induced structural modifications of thin film of vanadium pentoxide xerogels deposited on indium tin oxide (ITO)-coated glasses have been studied. Vanadium pentoxide xerogel has been prepared by using the sol-gel proton exchange resin route without any resin pretreatment. To monitor the effect of the 'resin efficiency' on the gelation process, the solution coming out from the resin has been collected in a sequence of different containers (vials), separately investigated by Raman spectroscopy. After the spin coating deposition, the thin films of vanadium pentoxide get have been subjected to different annealing treatments. The highest thermal treatment (600 degrees C) induces a complete transformation of the gel phase into an anhydrous polycrystalline phase of a sodium-containing vanadate, different from the usual V2O5 crystal. It is due to the diffusion of foreign ions (mainly sodium) coming from the substrate into the vanadium oxide layer.