EQUILIBRIUM OXYGEN VACANCY CONCENTRATIONS AND OXIDANT DIFFUSION IN GERMANIA, SILICA, AND GERMANIA-SILICA GLASSES

Equilibrium oxygen vacancy concentrations in 100% GeO2, 87 mol% GeO2-1 3 mol% SiO2, and 24 mol% GeO2-76 mol% SiO2 glasses were determined as a function of melting temperature and atmosphere, and the effects of o xygen and water in the atmosphere on the oxygen vacancy annihilation k inetics in these glasses were investigated, Equilibrium oxygen vacancy concentrations for a glass increased as the melting temperature incre ased, and decreased as the germania content of the glass decreased. Th e equilibrium vacancy concentration in 100% GeO2 was inversely proport ional to the square root of the oxygen partial pressure in the atmosph ere. Oxygen vacancy formation energies were approximately 2.5 eV. When 100% GeO2 and 87 mol% SiO2-13 mol% SiO2 glasses prepared by melting w ere heated, the glasses dehydrated, and the oxygen vacancy concentrati on was controlled by effective oxygen diffusion. Activation energies f or effective oxygen diffusion in 100% GeO2 and 87 mol% SiO2-13 mol% Si O2 glasses were 1.2 and 1.1 eV, respectively, A model for effective ox ygen diffusion is presented, which shows a dependency of the effective oxygen diffusion coefficient on the oxygen vacancy concentration. Whe n water-free 24 mol% GeO2-76 mol% SiO2 glass, prepared by CVD, was hea ted, the glass hydrated, and the oxygen vacancy concentrations were co ntrolled by effective water diffusion. As the germania content of the glasses increased, the effective water diffusion coefficients increase d. The presence of silica in the germania-silica glasses caused a kink to appear in the Arrhenius plots of effective water diffusion coeffic ients.