INTERACTION AND ORDERING OF LATTICE-DEFECTS IN OXYGEN-DEFICIENT RUTILE TIO2-X

The atomic and electronic structures of lattice defects in oxygen-deficient rutile TiO2-x (1 X 10(-4) less than or similar x less than or similar X 10(-3)) are discussed on the basis of electron-paramagnetic-resonance measurements. Titanium interstitials with a single paramagnetic electron (S = 1/2), which are the main lattice defects for small x (less than or similar 3 X 10(-4)), strongly interact with each other for large x (greater than or similar to 4 X 10(-4)) resulting in Ti interstitial pairs with two paramagnetic electrons (S = 1) whose Ti-Ti distance and orientation are 3.25 angstrom and [110], respectively. At the same time, a considerable fraction of the Ti interstitials are ordered in cooperation with an oxygen deficit, resulting in {121} plane defects. The (121) plane defect contains Ti-ion pairs whose Ti-Ti orientation is [100], and the Ti-ion pair has two covalent-bond electrons and an additional paramagnetic electron (S = 1/2).