Relaxation behavior of silver–sodium interdiffusion in a boroaluminosilicate glass

It is shown that interdiffusion of silver into a well-annealed sodium boroaluminosilicate glass can induce significant relaxation of the host glass at temperatures well below the transition temperature, Tg. The relaxation is manifest as a time-dependent interdiffusion coefficient which is shown to increase as the time of diffusion varies from 1.5 to 30 h. The presence of Ag is required for the observed relaxation; differential scanning calorimeter (DSC) scans and 22Na radioisotope-tracer diffusions indicate that the base glass is fully annealed before interdiffusion. An estimate of the characteristic relaxation time is given. Inclusion of the time-dependence is required to predict refractive index distributions within tolerance allowed for micro-optics applications, as shown by simulation.