Encroachment of titanium oxide on Ni surface for Ni/TiO2 under reducing atmosphere

The Ni-titania (TiO2) system was investigated to understand the phenomenon of titania encroachment on Ni surface as a function of temperature and oxygen partial pressure (PO2) under reducing atmosphere. A network-structured Ni film with widths of about 10 μm was prepared on titania. It is found that encroachment of non-stoichiometric TiO2 − x to the Ni surface occurs when TiO2 is reduced to TiO2 − x with random point defects, as the PO2 is within the range defined by Ni-NiO and TiO2 − x-TinO2n − 1 equilibria. On the other hand, no encroachment to the Ni surface occurs at much lower PO2, where TiO2 is reduced further to the Magneli phase TinO2n − 1 with ordered shear structure. A possible driving force for TiO2 − x encroachment to the Ni surface may be attributed to the high surface energy of TiO2 − x with disordered point defects. Furthermore, these results indicate the possible role of fast Ti diffusion in TiO2 − x which drives its encroachment to the Ni surface.