Structural factors in silver-induced relaxation in aluminosilicate glasses

The effect of the duration of diffusion is investigated in boroaluminosilicate and aluminosilicate glasses with varying non-bridging oxygen (NBO) contents. Silver/sodium interdiffusion coefficients are measured using energy-dispersive X-ray spectroscopy (EDX) and the Boltzmann–Matano method in glasses that have been ion-exchanged for 1.5, 5, 30, 75 and 120 h at 350 °C. The interdiffusion coefficient is strongly time-dependent for the NBO-poor glass, but changes negligibly in the case of the NBO-rich glass. Radioactive tracer diffusion coefficients are also measured for the NBO-poor glass using 110mAg and 22Na radioisotopes. The tracer coefficients are also time-dependent. We show that the cross-coefficients, which are used to relate tracer and interdiffusion in this glass, vanish for long diffusion times. This behavior is interpreted in terms of changes in the local cation environments induced by the presence of the dopant cation, and relaxation of the associated intermediate range structure in the glass.