Substitutional and Interstitial Centers

Obviously, the equivalence (randomness) of the spatial distribution of the acceptor impurities (V4+ ions) in polycrystalline lattice, or its heterogeneity, should strongly affect electrophysical, photoelectrochemical and catalytic properties of nano- 

Samples of the ceramic polycrystalline Ti02 (rutile) doped electrodes of the VxTi . x02 composition were studied at different vanadium content (0.001 x 0,05) in [128, 129]. It was shown that at x 0,003 the EPR spectra perform a well resolved hyperfine structure (hfs) typical of V4+-doped rutile (Fig. 8.10), in which V4+ ions substituted Ti4+ ions in the crystal lattice. At 0.003 x 0.01, the dipolar broadening of the individual lines 8H occurred. At x 0.01, in parallel with continuing broadening of the hfs lines, a broad single line appears (Fig. 8.11). Its part in the spectrum increased with the increase of vanadium content. 

This single line (go = 1.935 0.005, AH 140 G) is usual for V4+ centers, which are coupled by strong spin-exchange interaction [23, 164], These V4+ ions are localized in some areas with high local concentration (V4+)s (the so called nano-phases - because of their probable size), which can be estimated from the exchange narrowing of a spectrum by the equation [23]  

Here Vs h Ks are frequency and the rate constant of a static spin exchange in a solid state correspondingly Ks = 1.810s s 1-(g-ion/l) 2 for vanadyl ions VOz+ in solutions frozen at 77 K, AH is the linewidth in Gauss, and (V4+)s is measured in mol/1. It was calculated 

Photo-sensitization of Ti02 electrodes by doping crystals with different transition metals was done in many works, e.g., [141, 165-172]. The results similar to ours (in 

---