Electron paramagnetic resonance spectroscopy of γ-radiation-induced paramagnetic centers in titania-bearing sodium silicate glasses

The electron paramagnetic resonance (EPR) spectra of gamma-irradiated titania-bearing sodium silicate glasses were quantitatively analyzed by using the spectral decomposition of the EPR spectra and categorizing it into two types of randomly oriented paramagnetic centers: the orthorhombic (HC1) center and the axially symmetric (HC2) center. The orthorhombic HC1 center was assigned to the Q(2) structural unit (the term Q(i) represents a SiO4 tetrahedron with i bridging oxygens), whereas the generation of the axially symmetric HC2 radical was expected in the case of the Q(3) unit. The relative amounts x(HC1) and x(HC2) of HC1 and HC, radicals mere evaluated using the obtained data of the measured EPR spectra for five gamma-irradiated glasses with titania contents in the range of 0-10 mol%. The strong increase of the HC2 relative abundance, from a value of 26% (for titania-free glass) to a value of 89% (obtained for glass with 1 mol% of titania) confirmed the preferred sensitivity of Q(2) units at low titania contents. Thus, titanium, which has a great absorption cross section, preferably entered the positions in the neighborhood of the Q(2) units. The semi-empirical Linear combination of atomic orbitals to form molecular orbitals by a self-consistent field (LCAO-MO-SCF) quasi-relativistic intermediate neglect of differential overlap (INDO) method was used to confirm this effect. Far titania contents of >1 mol%, the above-mentioned Effect was overwhelmed by the structural changes induced by titania in the silicate network, namely the diminishing of the Q(2) content. Only the axially symmetric HC, centers were present in the glasses with titania contents of >5 mol%.