Chemical Structure and Concentration Dependence of the Diffusion Coefficient in Silver/Sodium Ion-Exchanged Aluminosilicate Glasses

Abstract

Ion exchange is often used to alter the index of refraction of a glass to fabricate waveguide and micro-optics devices, usually resulting in a gradient index. However, in order to efficiently design such devices it is necessary to be able to accurately predict and control the ion exchange. One important complication that must be accounted for is the Mixed Mobile Ion Effect (MMIE), also known as the Mixed Alkali Effect, in which many of the glass properties vary from additivity when two species of monovalent cations are present. This effect, although extensively documented, is poorly understood. As a result, parameters and conditions for ion exchanges are usually determined through a tedious trial-and-error process. We have found that insight into ion-exchange processes, including the MMIE, can be gained from studies of glass structure. We have studied silver-for-sodium exchange in a series of aluminosilicate glasses, commercially important for ion-exchanged waveguides. In this work we relate the results of our previous structural studies to MMIE and the concentration dependence of the diffusion coefficient.