Equilibrium oxygen vacancy concentrations and oxidant diffusion in germania, silica, and germania-silica glasses

Abstract

Equilibrium oxygen vacancy concentrations in 100% GeO 2 , 87 mol% GeO 2 13 mol% SiO 2 , and 24 mol% GeO 2 76 mol% SiO 2 glasses were determined as a function of melting temperature and atmosphere, and the effects of oxygen and water in the atmosphere on the oxygen vacancy annihilation kinetics in these glasses were investigated. Equilibrium oxygen vacancy concentrations for a glass increased as the melting temperature increased, and decreased as the germania content of the glass decreased. The equilibrium vacancy concentration in 100% GeO 2 was inversely proportional to the square root of the oxygen partial pressure in the atmosphere. Oxygen vacancy formation energies were approximately 2.5 eV. When 100% GeO 2 and 87 mol% SiO 2 13 mol% SiO 2 glasses prepared by melting were heated, the glasses dehydrated, and the oxygen vacancy concentration was controlled by effective oxygen diffusion. Activation energies for effective oxygen diffusion in 100% GeO 2 and 87 mol% SiO 2 13 mol% SiO 2 glasses were 1.2 and 1.1 eV, respectively. A model for effective oxygen diffusion is presented, which shows a dependency of the effective oxygen diffusion coefficient on the oxygen vacancy concentration. When water-free 24 mol% GeO 2 76 mol% SiO 2 glass, prepared by CVD, was heated, the glass hydrated, and the oxygen vacancy concentrations were controlled by effective water diffusion. As the germania content of the glasses increased, the effective water diffusion coefficients increased. The presence of silica in the germania-silica glasses caused a kink to appear in the Arrhenius plots of effective water diffusion coefficients.