The electronic properties of rutile TiO2 with an ordered arrangement of oxygen vacancies indicated a transition from a resistive to conductive oxide as a function of vacancy ordering. Vacancy ordering along two different directions [110] and [001], studied by the density functional theory, predicted that the geometries in which the vacancy-to-vacancy interaction was the strongest, within the nearest neighbor coordination, were thermodynamically favorable and of technological importance. The oxygen vacancies induce several occupied defect states of Ti3d character, and according to the present model, the vacancies were the mediators of electron conduction, while the conductive filament was formed by Ti ions. It was proposed that the formation of these types of conductive filament was intrinsically connected to the observed defect-assisted tunnelling processes and oxide breakdown issues.

Impact of Oxygen Vacancy Ordering on the Formation of a Conductive Filament in TiO2 for Resistive Switching Memory. Park, S.G., Magyari-Kope, B., Nishi, Y.: IEEE Electron Device Letters, 2011, 32[2], 197-9