SI-O-SI STRAINED BOND AND PARAMAGNETIC DEFECT CENTERS INDUCED BY MECHANICAL FRACTURING IN AMORPHOUS SIO2

Mechanical stress is applied to high-purity amorphous SiO2 samples by means of fracturing. The electron-spin-resonance spectra suggest that the formation of a majority of paramagnetic defects is from cleavage of Si-O-Si bridges in the glass network, but there are some sample-to-sample variances in fracture-induced paramagnetic defects, suggesting cleavage of differing chemical bonding states in the samples. Nonstoichiometric bonds, = Si-Si = and = Si-O-O-Si =, are assumed to be one reason for the sample dependency. Formation of Si-O-Si strained bonds from mechanical fracturing is confirmed from sequential gamma-ray irradiation and heat annealing experiments. The Si-O-Si strained bond is approximately annealed at about 300-degrees-C. By comparing the fracture-induced defects for glass preforms and optical fibers, the change in chemical bonding state can be analyzed. Analysis of mechanical-fracture-induced defects is a strong technique for elucidation of the chemical bonding state of silica glass.