Chemical annealing of oxygen hole centers in bulk glasses

Chemical annealing of the oxygen hole centers in bulk glasses by using hydrogen (or deuterium) has been extensively reported in the literature. Hydrogen chemically anneals these defect centers by reacting with them to form hydroxyl species. We have here presented a reaction-diffusion model to predict the chemical annealing rates of these defect centers in bulk glasses. The model considers diffusion of hydrogen (or its isotopes, e.g., deuterium) through the glass and its simultaneous reaction with the oxygen hole defect centers, resulting in the formation of the hydroxyl species in the glass. The predictions from the model are in excellent agreement with the experimental data presented in [J. Appl. Phys. 60 (12) (1986) 4325]. The model also establishes the precise connection between the dependence of effective hydrogen diffusivity on its intrinsic diffusivity, temperature, hydrogen and defect concentration. We also discuss methods for understanding chemical annealing behavior at high temperatures, where hydrogen not only reacts with the oxygen hole centers, but also with the silica matrix. For the case where hydrogen interaction with the silica matrix is the dominant reaction, a reaction-diffusion model is presented and the equilibrium constant (between 500 and 900 °C) for the reaction is estimated by comparing the predictions from the model with the hydroxyl profiles reported in [Appl. Phys. Lett. 47 (3) (1985) 328; J. Appl. Phys. 61 (12) (1987) 5447].