Electron Paramagnetic Resonance Spectroscopy of gamma‐Radiation‐Induced Paramagnetic Centers in Titania‐Bearing Sodium Silicate Glasses

Abstract

The electron paramagnetic resonance (EPR) spectra of ␥-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 (HC 1 ) center and the axially symmetric (HC 2 ) center. The orthorhombic HC 1 center was assigned to the Q 2 structural unit (the term Q i represents a SiO 4 tetrahedron with i bridging oxygens), whereas the generation of the axially symmetric HC 2 radical was expected in the case of the Q 3 unit. The relative amounts x(HC 1 ) and x(HC 2 ) of HC 1 and HC 2 radicals were evaluated using the obtained data of the measured EPR spectra for five ␥-irradiated glasses with titania contents in the range of 0-10 mol%. The strong increase of the HC 1 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. For titania contents of >1 mol%, the abovementioned 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 2 centers were present in the glasses with titania contents of >5 mol%.

Electron spin resonance in silicon substituted apatite and tricalcium phosphate

“…A summary of ESR spectra previously reported for defect centers in calcium phosphates is listed in Table 1. Centers have also been described in irradiated silica and silicate systems [18][19][20][21]. Table 2 lists the parameters of two centers, termed h1 and h2 observed in silicate glasses and crystalline compounds.…”