Intrinsic Point Defects in Oxides with the Rutile Structure

Abstract

The oxides which are of primary concern here have the rutile structure and are formed from elements of the fourth (Si, Ge, Sn, Ti) group of the Periodic Table. Instrinsic “point” defects of these oxides, oxygen and cation vacancies, cation interstitials and interstitial oxygen molecule ion complexes, have optical and magnetic properties which are a function of their charge state. Properties of the various charge states of oxygen vacancies can be described in terms of linear combinations of s and p states of nearest-neighbor cationswith the exception of TiO2, for which a linear combination of d orbitals of the three nearest-neighbor Ti ions is required. Paramagnetic states of oxygen vacancies in these oxides have been observed, and comparison of their properties and rates of production by reactor irradiation exhibits many differences. Electron paramagnetic resonance spectra which have been observed for singly charged oxygen vacancies in glassy SiO2 and GeO2 are compared with those produced in the rutile phases. Configurations of interstitial oxygen ions have several forms, data about which have been derived from electron paramagnetic resonance spectra. Definitive models which have been deduced in a few cases, e.g., O >2 - and O 3 - molecule ions, are discussed. Some reasons for the failure to detect either optical absorption bands or paramagnetic states of interstitial cations, with the exception of Ti3+ and interstitial oxygen ions in the case of TiO2 are discussed.