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 (P-O2) under reducing atmosphere. A network structured Ni film with widths of about 10 mu m was prepared on titania. It is found that encroachment of nonstoichiometric TiO2 - x to the Ni surface occurs when TiO2 is reduced to TiO2 (-) (x) with random point defects, as the P-O2 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 P-O2 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. (C) 2016 Elsevier B.V. All rights reserved.