Study of the phase transition and the thermal nitridation of nanocrystalline sol-gel titania films

Nanocrystalline titania films were prepared by a complexing agent-assisted sol-gel method and converted to titanium nitride by a thermal nitridation process. The effect of acetylacetone (AcAc), diethanolamine (DEA) and acid catalysts (HCl and HNO₃) on the structure and morphology of the heat-treated titania films and on their nitridation products was examined by FTIR spectroscopy, X-ray diffraction (XRD) and atomic force microscopy (AFM). The carbothermal reduction of titania during the nitridation process with the formation of carboxynitrides has been considered. The results showed that the oxide to nitride transition strongly depends on the complexing agent used to prepare the titania films. The XRD results indicated the dependence of the lattice parameter of the nitridation product on the complexing agent or acid catalyst: AcAc and DEA lead to TiN_x with a lattice parameter α close to the theoretical value, while with HCl the lattice parameter was found sensibly lower showing the presence of an oxynitride. These results are accounted for by the effect of complexing agents and acid catalysts on the size of both TiO₂ and TiN grains and the different reactivity of the anatase and rutile phases. The possibility of tailoring the composition and morphology of TiN films by using complexing agents is envisaged.