New evidence for the point defect model of ion transport in glasses

Abstract

We have determined the alkali concentration within the surface region of a soda–lime silicate glass as a function of experiment time by X-ray photoelectron spectroscopy. It was measured intermittently under three experimental conditions described below, where the sample was subjected continuously to monochromatic X-rays, low energy electrons from the flood gun, or both. Significant enhancement of the sodium concentration was observed when the sample was subjected to X-irradiation. Our observations corroborate that, at any one instant, a fraction of the ions remains associated with charge compensating centers, and hence are not able to diffuse freely in the absence of irradiation. Accordingly, under most common conditions, the diffusion of ions in glass occurs by point defects similar to that observed in the extrinsic-association region of crystalline solids.