The atomic and electronic structures of lattice defects in oxygen-deficient rutile TiO2-x (x = 10-4 to 3 x 10-3) were discussed on the basis of electron-paramagnetic-resonance measurements. Titanium interstitials with a single paramagnetic electron (S = 1/2), which were the main lattice defects for small x (≲3 x 10-4), strongly interact with each other for large x (≳4 x 10-4) resulting in Ti interstitial pairs with two paramagnetic electrons (S = 1) whose Ti-Ti distance and orientation were 3.25Å and <110>, respectively. At the same time, a considerable fraction of the Ti interstitials was ordered in cooperation with an oxygen deficit, resulting in {121} plane defects. The (121) plane defect contained Ti-ion pairs whose Ti-Ti orientation was <100>, and the Ti-ion pair had two covalent-bond electrons and an additional paramagnetic electron (S = 1/2).

Interaction and Ordering of Lattice Defects in Oxygen-Deficient Rutile TiO2-x. Aono, M., Hasiguti, R.R.: Physical Review B, 1993, 48[17], 12406-14