Paramagnetic Defects in TiO2 Produced by Radiation

Single crystals of TiO₂, space group $D_{\text{4h}}^{14}$ , reactor irradiated at 140°K and measured at 78°K, without warmup, exhibit intense electron spin resonance spectra. The most intense component of these spectra has an orientation dependence expected of a substitutional site. Two other less intense components of the spectra could be associated with interstitial sites or perturbed substitutional sites. The concentration of each of these was ∼ 0.1, the concentration of the intense component. These three spectral components and a blue–black color were no longer observed after warming to 300°K. An additional radiation with ¹³⁷Cs gamma rays at 77°K gave a new intense resonance having an orientation dependence expected for an interstitial site. Weak satellite lines observed for one orientation were attributed to hyperfine interaction with ⁴⁷Ti and ⁴⁹Ti. Good agreement between the observed orientation dependence and that calculated from a spin Hamiltonian for which $\mathrm{S\hspace{0.17em}=\hspace{0.17em}}\frac{1}{2}$ and for which $D_{\text{4h}}^{14}$ point symmetry is used was found for each species. On the basis of concentration, $g$ values, and hyperfine interactions, the two most intense spectral components are attributed to singly charged oxygen vacancies and interstitial Ti³⁺ ions.