Vibrational Raman studies of particle induced damage in oxide glasses

Abstract

Radiation effects in oxide glasses are manifested by color center formation, densification, and atom displacements. Localized vibrational modes are sensitive to such phenomena and exhibit both dose dependent frequency shifts and intensity variations in measured Raman spectra of irradiated glasses. Both bulk and glass fiber samples of NaPO 3, Y(PO 3) 3, and SiO 2 were subjected to external 5.5 MeV alpha irradiation in a nitrogen glove box from either 238Pu or 244Cm sources. Since damage is induced in a ca. 20 μm surface layer, thin fiber samples were chosen to optimize surface effects. All glasses developed color centers upon irradiation observed in measured UV/VIS absorption spectra. Raman spectra of binary phosphate glasses reveal two strong bands assigned to symmetric stretching of network -P-O-P- groups and terminal -PO 2- groups which both exhibit dose dependent frequency shifts and intensity variations. Results indicate that the onset of radiation damage is manifested at nonbridging oxygen sites in the glass. The observation of nitrate stretching vibrations in alpha-irradiated NaPO 3, a glass known to contain significant surface absorbed water, suggests that moisture enhanced radiolysis of N 2 near the glass surface has occurred. This effect was not observed for the more durable yttrium containing glass. Raman spectra of alpha-irradiated fused silica show changes in accord with previously reported results for neutron compacted silica. Lines assigned to bonding defect modes in the glass intensify with increasing dose, while band intensities for network vibrational modes decrease exponentially. The implication of these results to induced microstructural changes in the glass following alpha irradiation will be discussed.