Figure 6:Room-temperature EPR spectra of the Ti3 + ions in sol– gel derived TiO2 powder (Spectrum “(a)”) corresponds to the fresh sample; all other samples were treated at 400°C for 15 min in either an oxygen flow spectrum “(b)”, an argon flow (spectrum “(c)”), or a hydrogen flow (spectrum “(d)”). Theg-factor for spectra (b)–(d) was 1.99860.004. For all samples, the magnetic-field modulation was 0.08 mT.